Measuring Usability: Percentile to Z-Score Calculator

Percentile to Z-Score Calculator
by Jeff Sauro | December 4, 2007 :: 56 Related Questions How useful was this calculator?
Avg. Rating: 90 ( 30 ) | 2 Comments

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Tag Name	#	Vote
Calculator	12
Normal Curve	9
Z-Score	9
Statistics	8
skew	7

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Proportion of Area	Z-Score

Two-Sided One-Sided	Decimal Points

Enter the area under the normal curve (a proportion between 0 & 1) and get the Z-critical value, one-sided or two-sided. See also the interactive Graph of the Standard Normal Curve

To convert a Z-Score into a percentage use the Z-Score to Percentile Calculator

A Note about the Calculations & Decimal Precision
The values presented in the graphs above are approximations derived from the work of Abramowitz & Stegun. If you need precision to more that 3 decimals you are encouraged to consult multiple published tables of Z-Values.

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Related Questions

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	A z score of 1.04 shows a percentage value of?
	In a 0ne-tail test (l side) with z score of 1.645, what are the percentages for critical value and non-critical value?
	What are the units of z-score?
	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.
	In the same set of data,can two or more elements have the same z score.
	What is the critical z score for a one tailed test with alpha = .01.
	The lowest 25% of the normal distribution falls below what z-score and t-score
	How do you calculate the z score for the raw score of 10 based on the following distribution: 8, 9, 15, 30, 7, 8 ?
	Having obtained the z score and then derived the percentage... what does the percentage tell you?
	z Scores lenths are measured in centameters, does it have to be converted to a different unit of measurment?
	How do you calculate a Z-score with a two-sided specification limit? What is the DPMO? I have a lower spec limit of -0.008 and an uppers spec limit of 0.008. The mean of the data is -0.00306 and standard deviation is 0.003642. What is the z-score and DPMO
	The variable Z has a standard Normal distribution. a) Find the number z that has cumulative proportion 0.85. b) Find the number z such that the event Z
	What percent of the time should this occur? (Z-Score) ?
	IQ tests generally have scores in which the mean is 100, and the standard deviation is 16. If your IQ score was 134, what percentage of the population would have a higher IQ than you?
	If you have a normal distribution of a random variable x, with a mean of 56 and standard deviation of 8: What is the probability that the random variable x will be within plus or minus 1 standard deviation of the mean?
	How do you calculate a z-score on discrete data?
	On a scale from 0 to 100, the mean level of economic development among the countries in the world is 65 and the standard deviation is 10. What proportion of countries in the world have economic development scores above 80?
	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?
	a score that is 8 points above the mean corresponds to a z-score=0.05 What is the population standard deviation?
	What is the difference between a Z-Scores and Process Sigma?
	Between what two values of Z will 88% of the middle data values fall between?
	My local coffee house sells Colombian coffee beans to supermarkets in bags labelled 100g each. The tolerance of the automatic filling machine, leads to weights of bags being approximately Normally distributed with standard deviation 5g. The target mean weight is set at 106g (i.e. the filling machine is set at 6% overfill). Find the percentage of bags which are below the labelled weight. Show the z-score. How do i work this out?
	what is the value of z score required for a 70% confidence interval?
	Alexa got 144 on her test which has a mean of 128 and a standard deviation of 34. What is her z-score?
	Find the probability that a randomly selected adult has an IQ that is less than 130
	why can you not have a z- score equaling 0/0 ? what is problematic with calcutlating a z-score for a data set of repeated entries?
	The grades on the midterm given in a large managerial stats class are normally distibuted with mean 75 and standard deviation 9. Instructors of this class wants to assign an A to top 10%, B to the next 10%, C to next 10%, D to next 10%, and an F to all scores below the 60th percentile. Find the lowest acceptable score within each established range. For example, the lowest acceptable score for an A is the score at the 90th percentile.
	What is the z value for 1.648?
	What does a z value mean?
	What does a Z-score look like on a graph?
	Can a z score be calculated by input of a proportion only?
	Where can I find a Z score chart ?
	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.
	A sample of PVC pipes coming off a production line were tested for pipe diameter size. The statistical results (in millimeters) were: Mean 300 Median 300 Mode 300 Standard Deviation 15 Range 90 Number in Sample 100 a) According to the Normal Rule, what percent of the pipes had diameters between 285 and 315? b) What would the range of pipe diameters need to be in order to capture 95% of the pipe diameters?
	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.
	What score would Sandra need to beat 91 percent of her mathematics class? The mean score was 73, and the standard deviation was 12.
	Site preparation for new housing developments for tracts of 40 houses is normally distributed with a mean of 250 workdays and a standard deviation of 25 workdays. a.Find the probability that the site will not be completed within 280 days b. The probability that the site is completed in less than 225 workdays or it takes more than 275 workdays
	I am conducting a ring test where 6 laboratories were asked to measure protein levels in the same flour sample. I then calculated the z score for each of their results ... z score obtined ranged from 0 to 1.7. Does the higher z score indicate that the laboratories are too far away from the norm and that they need to review their process or their staff (assuming that they are using the same test procedure)??
	You survey a sample of 10 college students to measure their racial prejudice using a scale of 0 (no prejudice) to 100 (extreme prejudice). Here are the scores you obtained. 10 43 30 30 45 82 12 26 24 35 Compute the mode, median, mean, and standard deviation for this sample. Is there a skew; and if so, is it positive or negative? What does this skew reveal about the dispersion in the sample.
	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?
	Find the number z that has cumulative proportion 0.8
	Jeff: Can you possibly share the actual formula you are using in this application to produce the Adjusted Wald calculations? Thanks
	How do you calculate z-scores from batting averages?
	If a distribution of test scores is normal with a mean of 78 and a standard deviation of 11, what percent of the area lies below 60
	what is the z-score that corresponds to the 20th percentile of the normal distribution
	how does altman build z-score? please send to my email the process of building this score!
	How can I calculate a Z score with only the mean and the standard deviation?
	What is the basic formula for the z-score other than table of areas?
	With a z score of 1.5, what percentage often scores are above 52 and what percentage of the scores are above 60?
	How unusual is this event (Z-Score)? A department store, on average, has daily sales of $28,707.47. The standard deviation of sales is $1000. On Tuesday, the store sold $34,650.77 worth of goods. Find Tuesday's z score. Was Tuesday an unusually good day?
	The mean on this test is 3.5 with a standard deviation of .5. Billy scores 5. What is the standard score?
	Suppose that the scores of architects on a particular creativity test are normally distributed.What percentage of architects have Z scores. (a) above .10, (b) below .10, (c) above .20, (d) below .20, (e) above 1.10, (f) below 1.10, (g) above -.10, (h) below -.10?
	How do you find a z score such that 8% of the area under the curve is to the right of Z?
	Joe received a z score of -1.50 on a classroom test. This means that, compared to his classmates, Joe's score was...?
	If last six month average defect rate is 5% then what will be the process Zst score?
	I have a data set where n=20. My problem is to find the score at exactly the 75th percentile assuming normality. I know the formula for z-score, the mean, and the standard deviation. How do I do this problem?

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February 21, 2008 | anonomous wrote:

Hi - it would be reassuring if you could also generate a pictorial representation. Otherwise, very handy tool; thanks

February 20, 2008 | jim gillett wrote:

How can I find the mean and standard deviation if all I know is the percent under the curve and two of the actual data points

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