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| # | | Question | Helpful Rating | Tags |
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A central university has a student population of 60,000. The university is interested in determining what proportion of them is in favour of a new grading system. Determine a sample size with confidence level of 95% that will show the true proportion of population in favour of the new system within plus and minus 0.02. | | Margin of Error, Confidence Intervals, Sample Size |
| 470 |
 |
A telescope manufacturer wants its telescopes to have standard deviations in resolution to be significantly below 2 when focusing on objects 500 light-years away. When a telescope is used to focus on an object 500 light years away 30 times, the sample standard deviation turns out to be 1.46.
a.State explicit null and alternate hypotheses
b.Test your hypothesis at the á=0.01 level. | | |
| 469 |
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Mean output of solar cells of three types are measured six times under random light intensity over a period of 5 minutes, yielding the results shown. Research question: Is the mean solar cell output the same for all cell types? | | |
| 468 |
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just want to get updates on new articles....thanks. | | |
| 467 |
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62The Web-based company Oh Baby! Gifts has a goal of processing 95 percent of its orders on the same day they are received. If 485 out of the next 500 orders are processed on the same day, would this prove that they are exceeding their goal, using á = .025? | | |
| 466 |
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Biting an unpopped kernel of popcorn hurts! As an experiment, a self-confessed connoisseur of cheap popcorn counted 773 kernels and put them in a popperAfter popping, the unpopped kernels were counted. There were 86. (a) Construct a 90 percent confidence interval for the proportion of all kernels that would not pop. (b) Check the normality assumption. (c) Try the Very Quick Rule. Does it work well here? Why, or why not? (d) Why might this sample not be typical? | | |
| 465 |
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48 A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages On each page, the mean area devoted to display ads was measured (a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below
0 260 356 403 536 0 268 369 428 536
268 396 469 536 162 338 403 536 536 130
(a) Construct a 95 percent confidence interval for the true mean b) Why might normality be an issue here? (c) What sample size would be needed to obtain an error of ±10 square millimeters with 99 percent confidence? (d) If this is not a reasonable requirement, suggest one that is. | | |
| 464 |
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How do you know when to use a t-score instead of a z-score and vice versa? | | Z-Score, t-score |
| 463 |
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Find the probability of correctly answering the first 2 questions on a multiple choice test if random guesses are made and each question has 3 possible answers. | | Multiplication Rule |
| 462 |
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Olympic Track related question: You know the last 5 race times at the same distance for 8 runners competing in a race. As such, you can calculate the mean, sd, and variance for each. How would you go about calculating the % each one has of winning based on these statistics, assuming normal distribution | | Z-Score |
| 461 |
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My question is on Measurement system analysis (MSA).
My metric is lead time.
I calculated it from the system (computer database) which stores all this information.
As I see it, my MSA should involve an accurate definition of the lead time listing the elements used to calculate the lead time in the system( computer database). What else is missing in my MSA interpretation ? Do I need to do a gage R&R ? | | Gage R&R |
| 460 |
|
20% kids danced. If 10 were selected at random, find probability that exactly four danced. | | BINOMDIST, Binomial pmf |
| 459 |
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How do you calculate a participant score if she was at the 67th percentile? I only have the standard deviation of the population and the mean. s = 27 x = 448.95 | | Percent Score, Percentile, Z-Score |
| 458 |
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In 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security-related jobs, and found that 1,143 were positive. (a) Construct a 95 percent confidence interval for the population proportion of positive drug tests. (b) Why is the normality assumption not a problem, despite the very small value of p? | | Confidence Intervals, Normality Assumption |
| 457 |
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What is a simple but legitimate power analysis formula? I am trying to do qualitative research on African American HS boys in the Midwest. I am using nominal variables and I want to have roughly 75-90 participants. Would this be enough for power? What formula? | | |
| 456 |
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I am trying to find out if a difference between two response sets is significant. I asked 98 boys what modalities they thought were attractive to girls. 35 said "athletes"; 25 said "tough guys." The rest endorsed other modalities at lesser rates. Any help would be greatly appreciated | | 2-proportion test |
| 455 |
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Assume scores are normally distributed with a mean of 10 and std dev of 2. Find the first quartile Q1, which is the score separating the bottom 25% from the top 75%. | | Quartile |
| 454 |
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what concerns arise from using formulae to calculate standard scores | | |
| 453 |
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A central university has a student population of 60,000. The university is interested in determining what proportion of them is in favour of a new grading system. Determine a sample size with confidence level of 95% that will show the true proportion of population in favour of the new system within plus and minus 0.02.
A telescope manufacturer wants its telescopes to have standard deviations in resolution to be significantly below 2 when focusing on objects 500 light-years away. When a telescope is used to focus on an object 500 light years away 30 times, the sample standard deviation turns out to be 1.46.
a. State explicit null and alternate hypotheses
b. Test your hypothesis at the á=0.01 level | | |
| 452 |
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why does a z score always have a mean of 0 and a standard deviation of 1? | | Standard Normal Curve |
| 451 |
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A sample of the math test scores of 35 fourth-graders has a mean of 82 with a standard deviation of 15.
Find the 95% confidence interval of the mean math test scores of all fourth-graders.
Find the 99% confidence interval of the mean math test scores of all fourth-graders.
Which interval is larger? Explain why. | | Confidence Intervals, Confidence Level |
| 450 |
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A researcher is interested in estimating the average salary of fire fighters in a large city. He wants to be 95% confident that his estimate is correct. If the standard deviation is $1050, how large a sample is needed to get the desired information and to be accurate within $200? | | Margin of Error, Sample Size |
| 449 |
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A telescope manufacturer wants its telescopes to have standard deviations in resolutin to be significantly below 2 when focusing on objects 500 light years away. When a telescope is used to focus on an object 500 light years away 30 times, the sample standard deviation turns out to be 1.46
a) state explict null and alternative hypotheses
b) Test your hypothesis at the alpha=0.01 level. | | a central university |
| 448 |
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central university has a student population of 60000. The university is interested in determining what proportion of them is in favor of a new grading system. determine the sample size with confidence level of 95% that will show the true proportion of population in favour of the new system with plus and minus 0.02. | | |
| 447 |
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If he correlaion between X and Y is equal to -1.0, what do we know about the prediction of Y by X? (a)It's negative (b) It's postive (c)It's perfect (d)It's direct | | |
| 446 |
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When using two predictor variables, these variables should be (a)Correlated (b)Related (c)Independent (d) Dependent | 78.57 | |
| 445 |
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What must be used to examine an outcome that is predicted from two independent variables? (a)Multivariate regression (b)Multiple regression (c)Simple Regression (d)Complicated regression | | |
| 444 |
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What mut be done to categorical variables in order to use them in a regression analysis? (a)Nothing (b)Dummy coding (c)Problem coding (d)Categorical coding | 78.57 | |
| 443 |
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A postive trend line is associated with what type of slope? (a)Negative slope (b)Direct slope (c)Postive slope (d)Nondirectional slope | | |
| 442 |
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uSING THE REGRESSION FORMULA WITH SLOPE=.704 and intercept=.719, what would the predicted college GPA be for a student whose current high school GPA=3.2? (a)2.97 (b) 2.69 (c) 3.00 (d)3.20 | | |
| 441 |
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Which of the following Excel Function calulated the point at the regression line crosses the y-axis (a)SLOPE (b)CORREL (c)INTERCEPT (d)PEASON | | |
| 440 |
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How would you represent score of Y based on a known value of X? (a)Y (b)y-intercept (c)Y'(d)Y=Xa | | |
| 439 |
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I have a jar containing 100,000 marbles. There are 6 colors of marbles in the jar and they are present at frequencies of 2%, 2%, 4%, 10%, 57%, 25%. How do I determine my precision in estimating the true color frequencies in my jar at various sample sizes (I can't replace marbles)? For example, If I remove 500 marbles from the jar, what kind of precision will I have in estimating the frequency of a color that is actually present at 2%? | | |
| 438 |
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How do i compute for the standard score (z-score)of the following data? How will the graph look like?
53
53
50
45
45
43
42
42
41
40
39
39
39
38
37
36
36
36
36
34
34
32
32
32
32
31
31
30
30
29
28
27
27
26
18 | | |
| 437 |
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how can i interpret standard or z scores? | | |
| 436 |
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when is ecological correlation appropriate?
When is it not useful? | | Ecological correlation |
| 435 |
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Parametric and Nonparametric Data Identification Assignment
Label each of the following situations “P” if it is an example of parametric data or “NP” if it is an example of nonparametric data.
1. A manufacturer produces a batch of memory chips (RAM) and measures the mean-time-between-failures (MTBF). The manufacturer then changes a manufacturing process and produces another batch and again measures the MTBF. Did the change to the process improve the MTBF? ____
2. From a written survey where the respondents were asked to rate an individual on a scale of 1 to 5, one group rated an individual a 3.7, another group rated the individual a 4.3. Is the difference statistically significant? ____
3. A catering company is buying equipment in order to set up their own store. They have a choice of two ovens that they can purchase for the store. The used oven is $100 less than the new oven, but its heating calibration is off by 20 degrees. Which one is a better buy for them? ____
4. Jim Smith owns three real estate offices in Anytown. He has decided to open one more office, but he cannot decide between Hometown or Uptown as the town where he wants to locate. He will be comparing the mean number of homes sold per real estate agent, and the mean commission percentage earned by agents in the two towns to make his decision. ____
5. A study to determine if job absenteeism is distributed evenly over the week. ____
6. Mel’s Diner has been surveying their customers for the past couple of years about their dining experience in the restaurant. The survey uses a scale of one to five, five being best to indicate customer satisfaction. Mel’s customer satisfaction averaged 2.5 last year, but this year it is 2.9. Is this difference statistically significant? ____
7. Sally’s Beauty Salon just opened for business. Sally assigns the stylists customers on a rotation basis so that everyone is kept busy all day. One month after she opened the salon, Sally’s customer count for each stylist was (a) 20 customers; (b) 30 customers; (c) 15 customers; and (d) 25 customers. Has Sally been fair in how she allocates customers to each of the stylists? ____
8. A comparison of salaries between male and female employees in the same organization. ____ | | Non-Parametric, Parametric |
| 433 |
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My data set is non-normal (cycle time). Can I convert the data into "Good and Bad" based on a specification and then find a Z value to estimate my sigma level ? | | Cycle Time, Non-Normal Data, Log Transformation |
| 432 |
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Assume that the population of heights of male college students is approximately normally distributed with mean m of 68 inches and standard deviation s of 3.75 inches. A random sample of 16 heights is obtained.
Describe the distribution of x, height of the college student.
Find the proportion of male college students whose height is greater than 70 inches.
Describe the distribution of x(bar), the mean of samples of size 16.
Find the mean and standard error of the distribution.
Find P ( x(bar)> 70)
Find P ( x(bar)< 67) | 100 | TDIST, t-score |
| 430 |
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Individual scores of a placement examination are normally distributed with a mean of 84.2 and a standard deviation of 12.8.
If the score of an individual is randomly selected, find the probability that the score will be less than 90.0.
If a random sample of size n = 20 is selected, find the probability that the sample mean will be less than 90.0. | 100 | |
| 429 |
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A coin was flipped 60 times and came up heads 38 times. (a) At the .10 level of significance, is the
coin biased toward heads? Show your decision rule and calculations. (b) Calculate a p-value and
interpret it. | | |
| 428 |
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Each student in an experiment was told to look at 100 cars and count the number of people wearing the seat belts. The mean score for the class was found to be 44, and standard deviation =7. Now, a student reported finding 62 seat belt users out of 100. Do you think the student just made up a number rather than actually counting? | | Z-Score |
| 427 |
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Set up a model to test whether there are differences in mean ... DATA SET E Ages and Weights of 31 Randomly Chosen U.S. Nickels (n = 31 nickels) Nickels | | |
| 426 |
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can individual scores of a 542 student be converted into percentage and fed into spss for anova and tukey test | 50 | Percent Score, ANOVA |
| 425 |
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A real estate agent has 2 tours. The first tour through N1and has 10 homes for sale, whereas the second tour through N2and has 5 homes for sale. The real estate agent has already a good sense of the preferences P of her client. Approximately 20% of all homes in area N1satisfy her client’s criteria whereas in area N2approximately 80% of all homes will be suitable for her client.
[a] What is the probability to find in both neighborhoods a suitable house that satisfies the client's preferences?
[b] Give the posteriori probabilities of finding a suitable house for the client in either one of two neighborhoods. | | |
| 424 |
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A recent article in a computer magazine suggested that the mean time to fully learn a new software program is 40 hours. A sample of 100 first-time users of a new statistics program revealed the mean time to learn it was 39 hours with the standard deviation of 8 hours. At the 0.05 significance level, can we conclude that users learn the package in less than a mean of 40 hours?
a. State the null and alternate hypotheses.
b. State the decision rule.
c. Compute the value of the test statistic.
d. Compute the p-value | | 1-sample t-test, Alternative Hypothesis , Null Hypothesis , test statistic, p-value |
| 423 |
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the lengths of human pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days. What is the probability that a pregnancy lasts at least 300 days? | | Z-Score |
| 422 |
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A newspaper finds that the mean number of typographical errors per page is five. Find the probability that:
1. Exactly five typographical errors will be found on a page.
2. Fewer than five typographical errors will be found on a page.
3. No typographical errors will be found on a page. | | |
| 421 |
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A surgical technique is performed on eight patients. You are told that there is an 80% chance of success.
Construct a binomial distribution.
Find the mean, variance, and standard deviation of the probability distribution and interpret the results.
Find the probability that the surgury is successful for exactly six patients.
Find the probability that the surgury is successful for fewer than six patients. | | |
| 420 |
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In one region, the September energy consumption levels for single-family homes are found to be normally distributed with a mean of 1050 kWh and a standard deviation of 218 kWh. Find P45, which is the consumption level separating the bottom 45% from the top 55%. | | Z-Score |
| 419 |
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Suppose two events are independent. One event has probability of 0.25, while the other has probability of 0.59. | 100 | Multiplication Rule |
| 418 |
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Dear Stats Person,
Here is my question. If a person were to guess a number from 1-10, the chance of guessing a 4 would be 0.1. If 5 people were asked to guess a number from 1-10, the chance of guessing a 4 would be 0.5. The chance of 2 people guessing a 4 would be (0.1)(01.)=(0.01), correct? Shouldn't the total number of people also be accounted for? That is what is the chance of 2 people guessing a 4 out of 8 people? or 2 people guessing a 4 out of 20 people guessing? What about the chance of 3 people guessing 4 out of 50 people guessing? Is there a formula for this?
Thank you.
Diane | | BINOMDIST, Binomial Probability, Binomial pmf |
| 417 |
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Could you detail the value of using standard scores (Z scores) to compare relative performance of individual test scores. | | Z-Score |
| 416 |
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Twenty students randomly assigned to an experimental group receive an instructional program; 30 in a second group do not. After 6 months, both groups are tested on their knowledge. The experimental group has a mean of 38 on the test (with an estimated population standard deviation of 3); the control group has a mean of 35 (with an estimated population standard deviation of 5). Using the .05 level, what should the experimenter conclude? (a)Use the steps of hypothesis testing, (b) sketch the distributions involved, and (c) explain your answer to someone who is familiar with the t test for a single sample, but not with the t test for independent means. | | 2-sample t-test, Hypothesis Test |
| 415 |
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how do i find the lower 25% and upper 75% and the interquartile range | | Interquartile Range |
| 414 |
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If you have 100 respondents identifying their gender, what would be the expected frequency for each category? a)25 b)50 c)75)d)100 | 88.57 | |
| 413 |
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In order to meet the sample assumption associated with parametrics statistics, how many subjects do you need? a)20 b)30 c)50 d)100 | 85.71 | |
| 412 |
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If you have 30 espondents identifying their political preference(i.e.,Democrat, Republican, Independent),what would be the expected frequency for each category?
a)10 b)20 c)30 d)40 | 50 | |
| 411 |
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Do you have any hints how I can figure out critical values at the significance level? Can you figure this out in excel or megastat? Is there a equation? Would appreciate an answer. Thanks | | NORMSINV, TINV |
| 410 |
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You take a random sample of pizzas sold during a one hour period over the next week. Group 1 and Group 2 The results are shown in the table to the at the bottom of this. Does the ad campaign make a difference? Can you suggest a different methodology to test whether the ad campaign is effective?
Set up a model to test whether there are differences in mean satisfaction between groups. Use an alpha of .05
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Be sure to fully explain your conclusion. Please answer. Thanks
Pizza Sales
"Group 1
Pepperoni Mushroom Olive Slices sold with expensive ad campaign and promotion
" "Group 2
Hawaiian Slices sold without expensive ad campaign and promotion
"#1 Group 2
20 18
24 23
24 22
24 19
23 18
23 18
22 18
20 16
19 15
16 14 | | 2-sample t-test |
| 409 |
|
What is the height of a man with the z score of -1.7? | | Z-Score |
| 408 |
|
Use Excel, or MINITAB to fit the regression model, including residuals and standardized residuals:
DATA SET E Ages and Weights of 31 Randomly Chosen U.S. Nickels (n = 31 nickels) Nickels
Observation Age (yr) Weight (gm) Observation Age (yr) Weight (gm)
1 2 5.043 17 15 4.956
2 15 4.893 18 5 5.043
3 22 4.883 19 10 5.032
4 27 4.912 20 2 5.036
5 38 4.980 21 14 4.999
6 2 5.003 22 1 5.004
7 0 5.022 23 21 4.948
8 28 4.796 24 12 5.045
9 12 4.967 25 40 4.917
10 17 4.951 26 1 5.014
11 13 4.932 27 9 5.001
12 1 4.970 28 22 4.801
13 1 5.043 29 21 4.927
14 4 5.040 30 1 5.035
15 1 4.998 31 16 4.983
16 9 4.956
________________________________________
Source: Randomly chosen circulated nickels were weighed by statistics student Dorothy Duffy as an independent project. Nickels were weighed on a Mettler PE 360 Delta Range scale, accurate to 0.001 gram. The coin's age is the difference between the current year and the mint year. | | Minitab, Regression Analysis, Residuals |
| 405 |
|
Marge and Joe have five daughters. They decide to have another baby because they are sure the next one will be a boy (after all, what are the odds of having another girl!)
Is their reasoning accurate? Why or why not?
What is the probability of having six girls?
What is the probability of having five girls and one boy | | BINOMDIST, Multiplication Rule, Gambler's Fallacy, Probability Mass Function |
| 404 |
|
How do you calculate a standard deviation when your data is so large you can not enter it into the calculator. (I have 50 pcs of data) | | |
| 403 |
|
Based on information obtained from a sample of 54, a 98% confidence interval for the average profit level of regional banks is given by 67.4 million to 87.78 million. Determine the sample standard deviation of profit | | Standard Deviation, Margin of Error, Critical Value, Confidence Intervals, Confidence Level |
| 402 |
|
How can I compute a one-sided 97.5% confidence interval using SPSS for this ?
IN a cohort of 121 eyes treated with drug A, 3 eyes experience a drug related side effect, i.e 3/121. Thanks | | SPSS, Confidence Intervals, 1-sided Interval |
| 401 |
|
A woman wrote to DearAbby and claimed that she gave birth 308 days after a visit from her husband, who is in the Navy. Lengths of pregnancies have a mean of 268 days and a standard deviation of 15 days. Determine if such a length is considered unusual? | | Z-Score, Unusual Event |
| 400 |
|
What is the standard general score conversion formula? Is this the same as a z-score formula? Which leads me to ask How do you convert from one standard score to another? | 31.43 | Standard Score |
| 399 |
|
When you calculate CIs for time on task, I notice that you use the critical value from the t-distribution (TINV(0.05, degrees_of_freedom)). But when you calculate CIs for task completion rate (using the Adjusted Wald Method), you use the critical value from the z-distribution (1.96). Why don't you use the same value in both? | | exact interval, Binomial Probability, TINV, Adjusted Wald, Wald Interval, Normal Approximation, Small Sample |
| 398 |
|
What is the formula for the exclusive range?
What is the formula for the inclusive range? | | |
| 397 |
|
mean score 100,standard deviation 20, z score-5 , what is the raw score? | | Z-Score, Raw Score from Z-score |
| 396 |
|
what is the bottom of 20% of SAT | | |
| 395 |
|
What is the Variance, Standard Deviation and Range of the following set of scores? 20,24,26,22,18,16,18 and then 10,15,12,18,19,16,12 | | |
| 391 |
|
An engineer in an automotive factory wishes to know what the tire pressure is on all cars leaving the factory. She measures the tire pressure on a sample of 10 randomly selected cars as they are about to leave the plant, in psi. The results are:
32.1
32.3
32.0
30.9
31.5
32.4
32.9
33.1
32.2
31.4
Calculate a 95% Confidence Interval on these numbers | | Standard Error of the Mean, t-statistic, Confidence Intervals, Critical Value |
| 390 |
|
How do you find the normal distribution when the mean is 50 witha standard deviation between scores of 32 and 47? | | Area between, Z-Score |
| 389 |
|
How do you dertermine a z-score for continuous data? | | Z-Score |
| 388 |
|
In Dallas, some fire trucks were painted yellow (instead of red) to heighten their visibility. During a test period, the fleet of red fire trucks made 153,348 runs and had 20 accidents, while the fleet of yellow fire trucks made 135,035 runs and had 4 accidents. At á = .01, did the yellow fire trucks have a significantly lower accident rate? (a) State the hypotheses. (b) State the decision rule and sketch it. (c) Find the sample proportions and z test statistic. (d) Make a decision. (e) Find the p-value and interpret it. (f) If statistically significant, do you think the difference is large enough to be important? If so, to whom, and why? (g) Is the normality assumption fulfilled? Explain. | 100 | 2-proportion test, Binomial Probability, Normal Approximation |
| 386 |
|
I am calculating the effectiveness of an educational intervention using a pretest-posttest design. I plan to run an ANCOVA on the scores with the pretest as the covariate. The six subcatagories on the test give the raw score of correct answers out of the total possible on each subcatagories. The overall score is given as a scaled score to equalize any differences on the pretest and posttest versions. The number of questions in each subcatagory and the overall test vary from the pretest and the posttest. Do I need to convert the scores to z scores to run the ANCOVA or can I use a percent score for each subcatagory and the scaled score for the overall score? | | Covariate, ANCOVA, ANOVA |
| 385 |
|
Given that the traveling distance for a population of college students is normally distributed with the mean of 10 kilometers and standard deviation equal to 3: Use the normal distribution to solve the following.
a) what proportion live within 12 kilometers of the campus
b) what proportion live further than 15 kilometers from campus
c) what distance would give the closest 10%
d) what distance would give the furthest 33% | | Z-Score |
| 384 |
|
Test at the 5% level of significance whether the true mean time it takes for luggage to reach the travelers is less than 17 minutes. Determine the null hypothesis. / | | |
| 383 |
|
Briefly describe the concept of a confidence interval and provide an example. | 87.14 | Confidence Intervals |
| 381 |
|
If I know the T-score for those who made an A on a test is 60, the z-score for those that made a B is .5, the number of students total is 200, how can I find the number of students who made a B? | | Z-Score |
| 380 |
|
What is the relationship between the sign of the correlation coefficient and the sign of the slope of the regression line? | | Correlation, Regression Line |
| 379 |
|
1 a. with a mean of 300 and a standard deviation of 80, how high a score do you need to be in the top 30%?
1 b. What is the interquartile range for this distribution? | | Interquartile Range, Z-Score |
| 378 |
|
We have administered an anxiety test to all members of the class. The mean anxiety score is 71 and the standard deviation is 9. (higher score=higher anxiety)
What percentage of people scored over 86 on the anxiety test? | | Z-Score |
| 377 |
|
A sample of households that subscribe to the United Bell Phone Company revealed the following numbers of calls received by each household last week. Determine the mean, median, and standard deviation of the number of calls received.
52, 43, 30, 38, 30, 42, 12, 46, 39, 37, 34, 46, 32, 18, 41, 5 | | mean, Median, Standard Deviation |
| 376 |
|
What statistical tests can I perform to compare two groups asked the same question, when the question has a yes/no answer and the sample groups are different. | | 2-proportion test |
| 375 |
|
why are histograms more appropate than bar graphs | | |
| 374 |
|
Where do I start? I have two related questions for you.
1) A sample of size n = 14 is selected from a normal population to construct a 95% confidence interval estimate for a population mean. The interval was computed to be (7.82 to 9.64). Determine the sample standard deviation.
2) A machine produces 3 inch nails. A sample of 100 nails is selected, and it is found that 25 are shorter than 3 inches. Find the 95% confidence interval on the proportion of all such nails that are shorter than 3 inches. | | |
| 372 |
|
Can you please direct me to a site that would have an illustration of the normal curve that also includes cumulative percentiles, Z-score equivalents, T-score equivalents, SAT scaled score equivalents, etc. thanks | | SAT Scores, Normal Curve |
| 371 |
|
Can you give me a formula to calculate sample size? | | Sample Size, Margin of Error |
| 370 |
|
The accounting department at Weston reports that it takes two construction workers a mean of 32 hours and a standard deviation of 2 hours... Determine the z values for 29 and 34 hrs. What percent of garages take between 32 and 34 hrs to erect. | | Area between, Z-Score |
| 369 |
|
A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on very accurate scale. The results in grams were 3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477 (a)Construct a 90% confidence intervalfor the true mean weight. (b)What sample size would be necessary to estimate the true weight an error of +/- 0.03 gram with 90% confidence? | 78.57 | Margin of Error, Sample Size, Confidence Intervals |
| 368 |
|
in a random sample of 200 person of a town 120 are found to the tea drinker.In a random sample of 500 person of another town 240 are found to be tea drinker.Is the proprtion of tea drinker in the two towns are equal? use .001 level significance. | | Normal Approximation, 2-proportion test, Binomial Probability |
| 367 |
|
find the area under standard normal curve which lies (a) to the right of Z=1.76,(b)to the left of Z=.94,(c)to the right of Z=-.65,(d)b/w Z=.34 & Z=.62 | | Area between, Z-Score |
| 366 |
|
If I have 3 tables in the classroom with 16 girls and 8 boys in the class, what are the chances of 8 girls sitting at one table when seats are assigned randomly? | | |
| 364 |
|
A sample of 20 pages was taken without replacement from the 1,591-page phone directory Ameritech Pages Plus Yellow Pages. On each page, the mean area devoted to display ads was measured
(a display ad is a large block of multicolored illustrations, maps, and text). The data (in square millimeters) are shown below:
0 260 356 403 536 0 268 369 428 536
268 396 469 536 162 338 403 536 536 130
(a) Construct a 95 percent confidence interval for the true mean. (b) Why might normality be an
issue here? (c) What sample size would be needed to obtain an error of ±10 square millimeters with 99 percent confidence? (d) If this is not a reasonable requirement, suggest one that is. I am new at this and it would help if you could give me the formula and break it down step by step so I can understand. Thanks | | Margin of Error, Confidence Intervals, Sample Size |
| 363 |
|
A coin was flipped 60 times and came up heads 38 times. (a) At the .10 level of significance, is the coin biased toward heads? Show your decision rule and calculations. (b) Calculate a p-value and
interpret it. | | BINOMDIST, 1-Sample Proportion Test |
| 362 |
|
Popcorn kernels take between 100 and 200 seconds to pop. What sample size (number of kernels) would be needed to estimate the true mean seconds to pop with and error of 5 seconds and 95% confidence level? | | Small Sample, Sample Size, Margin of Error, Confidence Intervals |
| 361 |
|
If I have a formula that predicts the winners of football games and it picked 600 out of 20000 games with 70% of the 600 being winners how can I estimate the future winning percentage of the formula? Thanks. | | |
| 360 |
|
What does a negative z-score represent? eg. -0.381 | | |
| 359 |
|
You have a normal distribution and your subject has a z score = 0. What percentage of the group will be below your subject? | | |
| 358 |
|
In the same set of data,can two or more elements have the same z score. | | Z-Score |
| 357 |
|
Biting an unpopped kernel of popcorn hurts! As an experiment, a self-confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the unpopped kernels were counted. There were 86. (a) Construct a 90 percent confidence interval for the proportion of all kernels that would not pop. (b) Check the normality assumption. (c) Try the Very Quick Rule. Does it work well here? Why, or why not? (d) Why might this sample not be typical? | 50 | |
| 356 |
|
The mean weight of 500 students is 151 lbs and the standard deviation is 15 lbs. Assuming the weights are normally distributed, find out how many students weigh between 120 and 155 lbs. | | Area between, Z-Score |
| 355 |
|
If Range = (6 * Standard Deviation), can it be concluded that Data is normal | | Nomal Distribution, Probability Plot |
| 354 |
|
A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on
a very accurate scale. The results in grams were
3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477
(a) Construct a 90 percent confidence interval for the true mean weight. (b) What sample size
would be necessary to estimate the true weight with an error of ± 0.03 grams with 90 percent confidence?
(c) Discuss the factors which might cause variation in the weight of Tootsie Rolls during
manufacture. | | t-statistic |
| 353 |
|
A surgical technique is performed on eight patients. You are told that there is an 80% chance of success.
a) Construct a binomial distribution.
b) Find the mean, variance, and standard deviation of the probability distribution.
c) Find the probability that the surgury is successful for exactly six patients.
d) Find the probability that the surgury is successful for fewer than six patients | | BINOMDIST, Binomial Probability |
| 351 |
|
As an experiment, a self-confessed connoisseur of cheap popcorn carefully counted 773 kernels and put them in a popper. After popping, the unpopped kernels were counted. There were 86. a)Construct a 90% confidence interval for the proportion of all kernels that would not pop. b)Check the normality assumption. c) Try the Very Quick Rule. Does it work well here? Why, or why not? d) Why might this sample not be typical? | | Confidence Intervals |
| 350 |
|
A robot, when working properly, produces 5% or less defective items. whenever the robot produces more than 5% defective items, i needs repair. A random sample of 300 items taken from the production line contained 27 defective items. Test at 1% significance level whether or not the robot needs repairing | | Continuity Correction, Normal Approximation, binomial, 1-Sample Proportion Test |
| 349 |
|
A bank has determined that the monthly balances of savings accounts of its customers are normaly distributed with an average balance of $1200 and standard deviation of $250. What proportions of the customers have monthly balances less than $1000? | | Z-Score |
| 348 |
|
A random variable X is normal distributed with a mean of 250 and standard deviation of 50. Given that X = 175, what is its corresponding z-score?
Round off your answer to 2 decimal places. | 100 | Z-Score |
| 347 |
|
Why is population shape of concern when estimating a mean? What does sample size have to do with it? | | |
| 346 |
|
Why is population shape of concern when estimating a mean? | | |
| 345 |
|
What are the 5 steps involved in hypothesis testing using the traditional/classical method; Can you use a simple real world example to explain it to me, becaue I am really not getting it. | 100 | Null Hypothesis , Alternative Hypothesis , Hypothesis Test |
| 344 |
|
Explain the difference between testing a single mean and testing the difference between two means. What two assumptions must be met when one is using z test to test differences between two means? When can the sample standard deviations s 1 and s 2 be used in place of the population standard deviations s 1 and s 2 ? | | Standard Deviation, z-test, Normally Distributed, Homogeneity of Variance |
| 343 |
|
The following data show samples of three chain stores in three different locations in one town and the amount of dollars spent per customer per visit. At the 0.05 level, is there a difference in among the means?
Store A Store B Store C
30 42 30
14 28 14
22 20 20
18 35 16
26 49 15
25 28
36
24 | 100 | ANOVA |
| 342 |
|
In a one-way ANOVA, there are three treatments with n1 = 5, n2 = 6 and n3 = 5. The rejection region for this test at the 5% level of significance is____________ | -0 | ANOVA, F-statistic |
| 340 |
|
Hi Jeff,
You have lots of great info on your site; thanks! However, I'm trying to reconcile some different items and they seem to disagree. Can you tell me if I'm misunderstanding something? In this article you use the ex, "Here’s why. If five out of five users complete a task, you can be 95% confident that the completion rate could be as high as 100% but it also could be as low as 48%. In other words, if you tested another five users, their completion rate will fall somewhere between 48% and 100%. Or if you're testing 100 users, as many as 52 of the 100 could fail the task." But when I put those #s (5 of 5) into your "Confidence Interval Calculator for a Completion Rate", none of the confidence intervals it generates are as low as the 48% mentioned in the example from your article. | | |
| 339 |
|
My question is really about sample size. Say you work at a facility and want to perform an assessment of your safety culture – this would involve multiple topics of questions expecting answers like agree, tend to agree, not sure, tend to disagree, disagree. How would you estimate the sample size if your total facility population is only 80 persons? Would the manner in which you estimate the sample size be different if you used any combination of the following methods to conduct the assessment: a written survey, individual interviews, one on one observations, or focus groups? What if these assessments must be performed at eight different facilities that have no relationship to each other and each of their total populations range from 15-1000, with a mean of 153? To make it even more complicated, would the manner in which you estimate sample size change if you really wanted each of the facilities to assess eight work groups or divisions in the workforce (e.g., management, operations, maintenance, engineering, etc.) at each of their facilities? Greatly appreciate your input. | | Sample Size, Margin of Error |
| 338 |
|
Is the chi-square distribution is a skewed distribution whose mean value is n for degrees of freedom larger than two? | 98.57 | Chi-Square |
| 337 |
|
is the chi-square distribution used for inferences about the population mean when the standard deviation is unknown? | | Chi-Square |
| 336 |
|
Why is population shape of concern when estimating a mean? What does sample size have to do with it? | | Central Limit Theorem |
| 335 |
|
The random variable x has the following probability distribution.
x 1 2 3 4 5
P(x) 0.5 0.2 0.1 0.1 0.1
Find the mean and standard deviation of x. | 100 | Expected Value, Random Variable, Standard Deviation |
| 334 |
|
find the z value so that 20% of the standard normal curve lies to the right of Z | | Z-Score |
| 333 |
|
A woman sells an average of 300 books per month, with a standard deviation of 50. Over the next ten years, how many months will she sell more than 375 books? (round to the nearest month, if necessary) | | Z-Score |
| 332 |
|
If our decision in a hypothesis test is to fail to reject the null hypothesis, then do we know that the null hypothesis must be true? | 100 | Null Hypothesis |
| 331 |
|
When we reject the null hypothesis, we are certain that the null hypothesis is false ? | 100 | Null Hypothesis |
| 330 |
|
If you had a sample size of 50 and did not know the standard deviation of the population, would you use a t or a z statistics in your analysis? Why? | 100 | t-test, z-test |
| 329 |
|
A husband and wife make their decisions independently of each other, and then they compare their decisions. If they agree, the decision is made; if they do not agree, then further consideration is necessary before a decision is reached. Assume each has a history of making the right decision 70% of the time.
What is the probability that they together make the right decision on the first try? | 100 | Multiplication Rule |
| 327 |
|
Want a sample size of about 60 (30 controls and 30 cases). At 5% significance and 80% power.How do i determine the standard deviation and mean difference.And how do i arrive at the 60? my study design is case-control. | | Power, Standard Deviation, Mean Difference |
| 326 |
|
What statistic would be applied if the independant variable is nominal and one dependant variable is nominal and one dependant variable is scale? Is this a T-test? | | t-test |
| 325 |
|
A doctor knows from experience that 20% of the patients to whom he gives a high blood pressure drug will have undesirable side effects. Assume the doctor gives that drug to ten of his patients. Find the probability that among the ten patients to whom he gives the drug, at most two will have undesirable side effects. | 100 | BINOMDIST, Excel, Binomial Probability |
| 322 |
|
What effect does an increase in the level of confidence have on the width of the confidence interval? | 100 | Confidence Level |
| 321 |
|
A normal distributed population has a mean of 250 pounds and a standard deviation of 10 pounds. Given n = 20, what is the probability that this sample will have a mean value between 245 and 255 pounds? | | Area between |
| 320 |
|
Individual scores of a placement examination are normally distributed with a mean of 84.2 and a standard deviation of 12.8.
If the score of an individual is randomly selected, find the probability that the score will be less than 90.0.
If a random sample of size n = 20 is selected, find the probability that the sample mean will be less than 90.0. | 100 | t-score, TDIST |
| 319 |
|
A machine cuts circular filters from large rolls of material. If 7.3% of the filters fail to meet specifications, use the normal approximation to the binomial to compute the probability that a sample of 100 of the filters will contain 5 or fewer that fail to meet specifications. | 100 | binomial, Binomial Probability, Normal Approximation, Continuity Correction |
| 318 |
|
A traffic study at one point on an interstate highway shows that vehicle speeds are normally distributed with a mean of 61.3 mph and a standard deviation of 3.3 mph. If a vehicle is randomly checked, find the probability that its speed is between 55.0 mph and 60.0 mph. | 100 | Area between, Z-Score |
| 317 |
|
Can the bell curve probability value be over the value of 1? | | Normal Curve, Bell Curve |
| 316 |
|
Hello, I work in Aerospace Engineering. Aerospace components are often subjected to cyclic loads and can fail in "fatigue". The designers design the parts against fatigue failures using the "fatigue life" of the materials, typically obtained by testing the coupons under cyclic loads. The fatigue life is defined as the number of cycles to failure when subjected to a specific applied cyclic load level.
However, there can be a lot of scatter in the data. Therefore, to be conservative, the designer uses the "minimum fatigue capability" of the materials, which is typically the "1/1000", or the "-3 sigma" value. I would like to figure out the minimum number of coupons one needs to test to obtain either the 1/1000 value, or the "-3 sigma" value. Your help or suggestion for further readings would be much appreciated.
To me, the 1/1000 means one has to ensure that only 1 in 1000 parts has fatigue life less than or equal to the 1/1000 value, but I am lost as to how to obtain that value.
In my mind, to obtain the -3 sigma fatigue life, one could test, say, 10 coupons, calculate the mean value and the standard deviations. Then subtract 3 standard deviations from the mean value to obtain the -3 sigma value. However, one could do the same with 5 coupons or 20 coupons, but the -3 sigma value would be very different. So the question is, how does one determine the appropriate sample size to produce a representative (statistically significantly?) -3 sigma value? I think it depends on the type of distribution, and I would like to assume a normal distribution to keep things simple for now. | 100 | Sigma Level |
| 315 |
|
An engineer in an automotive factory wishes to know what the tire pressure is on all cars leaving the factory. She measures the tire pressure on a sample of 10 randomly selected cars as they are about to leave the plant, in psi. The results are:
32.1
32.3
32.0
30.9
31.5
32.4
32.9
33.1
32.2
31.4
Calculate a 95% Confidence Interval on these numbers | | Standard Error of the Mean, Standard Deviation, Confidence Intervals, Critical Value, t-statistic |
| 314 |
|
I am doing A/B testing on an ecommerce web site. I have been working on rule of thumb of 500 vistors through each page or 50 conversions on one of the page before ending the test and deciding which is the best page. I assume there is more scientific way of deciding when to end the test. How is this calculated | | 2-proportion test, A/B Testing |
| 313 |
|
3 methods, A, B, and C are available for teaching a certain industrial skill. Only one of these methods is used in teaching a particular worker. The failure rate is 20% for A, 10% for B, and 30% for C. However, B is a more expensive and hence is used only 10% of the time, while C is very cheap and is used 50% of the time. Suppose a worker was selected at random and failed to learn the skill correctly, what is the probability that the worker was taught using method A? | | Bayes Theorem , Conditional Probability, Addition Rule |
| 311 |
|
A random sample of 100 pumpkins is obtained and the mean circumference is found to be 40.5 cm. Assuming that the population standard deviation is known to be 1.6 cm, use a 0.05 significance level to test the claim that the mean circumference of all pumpkins is equal to 39.9 cm. 1. State the null hypothese 2. state the alternative 3. Identify the test statistic 4. Find the P-value 5. What is the conclusion regarding the null hypothesis? 6. What is the final conclusion that addresses the original claim? | | p-value, Null Hypothesis , Alternative Hypothesis , Z-Statistic, t-statistic |
| 310 |
|
Various temperature measurements are recorded at different times for a particular day. the mean of 20 degrees C is obtained for 40 temperatures on 40 different days. Assuming that the standard deviation = 1.5 degree C, test the claim that the population mean is 22 degree C. Use a significance level of 0.05. 1. Identify null hypothesis 2. Identify alternate hypothesis 3.What is the test statisitc? 4. Calculate the P-value 5. What is the conclusion regarding the null hypothesis 6. What is the final conclusion that addresses the original claim? | | |
| 309 |
|
A cereal company claims that the mean weight of the cereal in its packets is 14 ounces. The weights in ounces of the cereal in a random sample of 8 of it;s cereal packets are listed below. 14.6, 13.8, 14.1, 13.7, 14.0, 14.4, 13.6, 14.2 test the company's claim at the 0.01 significance level. Please show all work especially test statistic, calculation of P-value | | 1-sample t-test, TDIST, t-score, t-statistic |
| 308 |
|
1. Seller Company sold merchandise on account to Beyer Co., $17,850, terms FOB destination, 2/15, n/eom. The cost of the merchandise sold was $10,700.
2. Sellars Company paid transportation cost of $140 for delivery of merchandise sold to Beyers Co. on August 1.
5. Sellars Company sold merchandise on account to Beyer Co., $27,550, terms FOB shipping point n/eom. The cost of the merchandise sold was $16,500.
6. Beyer Co. returned $1,800 of merchandise purchased on account of August 1 from Sellars Company. The cost of the Merchandise returned was $1,050.
9. Beyer Co. paid transportation charges of $165 on August 5 purchase from Sellars Company.
15. Sellars Company sold merchandise on account to Beyer Co., $32,000, terms FOB shipping point, 1/10, n/30. Sellars Company paid transportation cost of $1,243, which were added to the invoice. The cost of the merchandise sold was $19,200.
16. Beyer Co. paid Sellars Company for purchase of August 1, less discount and less return August 6.
25. Beyer Co. paid Sellars Company on account for purchase of August 15, less discount.
31. Beyer Co. paid Sellars Company on account for purchase of August 5.
Instructions
Journalize the August transactions for (1) Sellars Company and (2) Beyer Co.
1. Study problem 6-6A. Prepare entries to record the transactions of August 1, 2, 6, 15, and 16 only. (Note: You need to prepare entries for both Sellars Company and Beyer Co.)
2.
Based on the following information contained in the table below, use FIFO procedures to calculate the gross profit earned on the sale of August 10. Assume a list price of $140 and a trade discount of 30%. Explain your answer.
purchases sales
date units unit cost total cost date units
1/10 10 48 480 2/10 8
2/15 100 54 5400 4/1 95
7/3 65 55 3575 8/10* 65
11/1 35 58 2035 11/15 30 | | |
| 305 |
|
How do I determine what test statistic to use if given a sample of test scores for a present year and a previous year using a .05 significance level to retain or reject the null hypothesis. | | |
| 304 |
|
Is a number whose z score is equal to zero equal to the mean? | 50 | |
| 303 |
|
This question was put to me the other day; "Whats the Z-score of 100?" my reply no enough info without the standard deviation or the mean I cannot calculate it.Any light you can shine on this will be greatly appreciated. | | |
| 301 |
|
the advantage of t-score over z-score | | t-statistic, t-score |
| 299 |
|
random variable x is normally distributed with mean of 250 and standard deviation of 50 find z-score for x=175 | | Z-Score |
| 298 |
|
a sample of 50 men with a mean of 35 and sd of 3.2 and alpha of .05, what is the z score, the critical value, the test value | | |
| 297 |
|
What is the formula for finding the t-statistic | | Newton-Raphson, t-statistic |
| 296 |
|
What is the Z value that corresponds to a probability of .05? | | |
| 295 |
|
How can I calculate a Z score with only the mean and the standard deviation? | | Z-Score |
| 294 |
|
A test is normally distributed with a mean of 40 and a standard deviation of 7. (a) What score would be needed to be in the 85th percentile? | | Z-Score, Percentile, Percentile Rank |
| 293 |
|
How can you use a Z score to interpret data in a school | | Z-Score |
| 291 |
|
According to the standard normal curve, _____% of values should fall;
within +/ – 1 standard deviation(s) from the mean;
+/- 3 standard deviations from the mean _________;
+/- 3.5 standard deviations from the mean__________? | | Standard Normal Curve, above .10 |
| 290 |
|
An auditor reviewed 25 oral surgery insurance claims from a particular surgical office, determining that the mean out-of-pocket patient billing above the reimbursed amount was $275.66 with a standard deviation of $78.11. (a) At the 5 percent level of significance, does this sample prove a violation of the guideline that the average patient should pay no more than $250 out-of-pocket? State your hypotheses and decision rule. (b) Is this a close decision? | 100 | Z-Score, 1-sample t-test, 1-sample Z-test, Standard Error of the Mean |
| 289 |
|
A standard I.Q. test produces normally distributed results with a mean of 100 and a standard deviation of 15. If an average I.Q. is defined to be any I.Q. between 90 and 109, find the probability of randomly selecting an I.Q. which is average. | 100 | Z-Score, IQ Score |
| 288 |
|
Twenty-seven users completed a task, and each user did so with a combination of two variables, S and V, which can each have a value of "yes" or "no". Pass/fail data was collected for each user with the following results:
S=yes, V=yes: 7/8 users passed
S=yes, V=no: 1/4 users passed
S=no, V=yes: 10/10 users passed
S=no, V=no: 4/5 users passed
How would one determine which combination of variables is the best (with statistical significance)? If that's not possible, can we show that one combination is statistically significantly worse than the others? What method would be used? | | Newton-Raphson, Logistic Regression, Maximum Likelihood |
| 287 |
|
