Reference table
Adjusted Wald intervals for small-sample completion rates
A lookup table of 95% adjusted Wald confidence intervals for common usability test results, from 4 of 5 to 70 of 100 completions. It shows how wide the range is with 5 to 20 participants and why getting to about 10 points either side takes around 100. The values are calculated with the adjusted Wald method from Agresti and Coull, which Sauro and Lewis recommend for small-sample completion rates. Report the observed rate with its interval.
Where this appears
What's in this reference table
| Observed | Completion rate | 95% adjusted Wald interval |
|---|---|---|
| 4 of 5 | 80% | 36% to 98% |
| 5 of 5 | 100% | 51% to 100% |
| 7 of 10 | 70% | 39% to 90% |
| 9 of 10 | 90% | 57% to 100% |
| 10 of 10 | 100% | 68% to 100% |
| 14 of 20 | 70% | 48% to 86% |
| 70 of 100 | 70% | 60% to 78% |
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<a href="https://www.koji.so/visuals/adjusted-wald-confidence-intervals-completion-rates-table"><img src="https://www.koji.so/visuals/adjusted-wald-confidence-intervals-completion-rates-table/adjusted-wald-confidence-intervals-completion-rates-table.png" alt="Table of 95% adjusted Wald confidence intervals for usability completion rates, showing that 5 of 5 successes fits a true rate as low as 51%." width="1200" height="781" /></a>
<p>Source: <a href="https://www.koji.so/visuals/adjusted-wald-confidence-intervals-completion-rates-table">Adjusted Wald intervals for small-sample completion rates</a>, Koji</p>
