## Improving the Prediction of the Number of Usability Problems

###### By Jeff Sauro, PhD and Jim Lewis, PhD . October 27, 2020 . Tags: Usability Problems, Sample Size, Usability Testing

Paraphrasing the statistician George Box, all models are wrong, some are useful, and some can be improved. In a recent article, we reviewed the most common way of modeling problem discovery, which is based on a straightforward application of the cumulative binomial probability formula: P(x≥1) = 1 - (1-p)n. Well, it’s straightforward if you like playing around with these sorts of formulas like Jim and