Jeff Sauro • January 4, 2008

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.

The Experiment Requires That You Continue: On The Ethical Treatment of Users

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Why you only need to test with five users (explained)

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What five users can tell you that 5000 cannot

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A Brief History of the Magic Number 5 in Usability Testing

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Confidence Interval Calculator for a Completion Rate

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Quantifying the User Experience: Practical Statistics for User ResearchThe most comprehensive statistical resource for UX Professionals Buy on Amazon | |

Excel & R Companion to Quantifying the User ExperienceDetailed Steps to Solve over 100 Examples and Exercises in the Excel Calculator and R Buy on Amazon | Download | |

A Practical Guide to the System Usability ScaleBackground, Benchmarks & Best Practices for the most popular usability questionnaire Buy on Amazon | Download | |

A Practical Guide to Measuring Usability72 Answers to the Most Common Questions about Quantifying the Usability of Websites and Software Buy on Amazon | Download |

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