Quantitative Usability, Statistics & Six Sigma by Jeff Sauro
Sample Size Calculator for a Completion Rate
by Jeff Sauro | January 4, 2008 ::
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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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| July 8, 2009 | Amir Raza wrote: |
| how we compute sample size for median(IQR) comparison between groups |
| June 24, 2009 | Ofori Boateng wrote: |
| I am about looking to determine my sample size of how many managers I should select to from six companies for my survey so that my sample size and frame will be valid. Unfortunately I do not have the total number of managers that are working for these phone companies in Ghana and it is becoming increasing difficult for me to find the numbers. Is there a way for me to determine this unknown sample size. The tpye of managers I need for my survey are those in operations research, financial operations, and makerting department. Please try and help me here. Thank you. Ofori Boateng |
| June 6, 2009 | Thomas Smith wrote: |
| ) "Why is population shape of concern when estimating a mean? What does sample size have to do?" |
| June 6, 2009 | Thomas Smith wrote: |
| The mean of a data sample, size n, forms an approximately normal distribution. ... Sample size n is about 30 to be sure that the central limit theorem applies. |
| June 6, 2009 | Thomas Smith wrote: |
| 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? |
| June 6, 2009 | Thomas Smith wrote: |
| 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. |
| April 16, 2009 | Brad Woodruff wrote: |
| What is the best way to calculate sample size for an incidence rate, such as a mortality rate? |
| February 10, 2009 | theresa wood wrote: |
| 3. 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? |
| May 17, 2008 | Chris wrote: |
| How do you calculate a confidence interval when the population standard deviation is unknown? |