Measuring Usability: Sample Size Calculator for a Completion Rate

Sample Size Calculator for a Completion Rate
by Jeff Sauro | January 4, 2008 :: 27 Related Questions How useful was this calculator?
Avg. Rating: 11 ( 1 ) | 1 Comments

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Tag Name	#	Vote
Sample Size	19
Confidence Intervals	15
Completion Rate	13
Calculator	12
Graph	3

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Use this calculator to understand how sample size changes will affect the confidence interval around a completion rate. For more context, see the Sample Size article.

Known Users: Most Likely Completion Rates

Known Minimum Completion Rate: Unknown Users

The calculations are derived from the Adjusted-Wald binomial confidence interval.

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Related Questions

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	When calculating confidence interval estimates...how is the x and standard deviation calculated?
	Why don't statisticians calculate 100% confidence intervals?
	Briefly describe the concept of a confidence interval and provide an example.
	how to calculate one sided 95% confidence limits for a proportion.could you provide a formula
	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?
	State the main points of the Central Limit Theorem for a mean. B. Why is population shape of concern when estimating a mean? What does sample size have to do with it?
	I am trying to do A/B testing onweb page displays. One is the test the other is the control. Could you help me determine the formula for sample size at a 95% confidence level? My historical Conversion Rate (success): 11% Visitors: 280 per day I would like to see a 2% improvement in my conversion rate.
	What is the Z score of a 98% confidence interval?
	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?
	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.
	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?
	The 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? (See story.news.yahoo.com accessed June 25, 2004.)
	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.
	How do you determine the sample size for data for which the mean and standard deviation are not known?
	How would I figure out a 90% and 95% confidence interval for the below informaion? What would be the formula? Can I figure this out in Excel or Megastat? How would I do that? Men Female count 53 47 mean 36,492.92 24,451.51 sample variance 340,313,003.72 154,893,232.30 sample standard deviation 18,447.57 12,445.61 standard error of the mean 2,533.97 1,815.38
	Annual starting salaries for college graduates with degrees in business administration are generally expected to be between $30,000 and $45,000. Assume that a 95% confidence interval estimate of the population mean annual starting salary is desired. What is the planning value for the population standard deviation (0 decimals)?
	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
	A random sample of 25 households finds that an average of 2.3 people reside in each house (the standard deviation is 0.35). With a 95% confidence level, what is your estimation of the population average?
	Jeff: Can you possibly share the actual formula you are using in this application to produce the Adjusted Wald calculations? Thanks
	In 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security relatd jobs and found that 1,143 were positive a. construct a 95% confidence interval for the population proportion of positive drug test. b. why is the normality assumption not a problem, despite the very small value?
	what is the value of z score required for a 70% confidence interval?
	How to determine the sample size for comparing mulltiple parameters like Height , weight, Blood pressure , Blood parameters like blood glucose, total cholesterol, etc in two different populations?
	If 350 respondents out of a random sample of 1,000 Americans reported that they did not trust their government, what is your estimation at a 99% confidence level of the proportion of the American population who do not trust their government?
	in a sample of 1000 tv vieweres 330 watched a particlar programme. find 99 pecent confidence limits for tv viewers who watched this programme
	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
	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?
	I am charged with sampling expense report submissions for accuracy. We get 8000 T&E claims, and want to sample a subset making inferences about the population. I can probably get a good estimate of the populations' SD, how would i calculate required sample size? I think i would be measuring the delta between actual and claimed - the majority be 0. Is this a one sided issue? Thanks in advance - FT Also, would i need the acceptable level first? ie. we would accept an average difference of $5? How can i work backwards if the first sample size yields an average of $1? (if that made sense)

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May 17, 2008 | Chris wrote:

How do you calculate a confidence interval when the population standard deviation is unknown?

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