Every estimate we make from a sample of customer data contains error. Confidence intervals tell us how much faith we can have in our estimates. Confidence intervals quantify the most likely range for the unknown value we’re estimating. For example, if we observe 27 out of 30 users (90%) completing a task, we can be
Confidence intervals are your frenemies. They are one of the most useful statistical techniques you can apply to customer data. At the same time they can be perplexing and cumbersome. But confidence intervals provide an essential understanding of how much faith we can have in our sample estimates, from any sample size, from 2 to
You don’t need a PhD in statistics to understand and use confidence intervals. Because we almost always sample a fraction of the users from a larger population, there is uncertainty in our estimates. Confidence intervals are an excellent way of understanding the role of sampling error in the averages and percentages that are ubiquitous in
Adding confidence intervals to completion rates in usability tests will temper both excessive skepticism and overstated usability findings. Confidence intervals make testing more efficient by quickly revealing unusable tasks with very small samples. Examples are detailed and downloadable calculators are available. Are you Lacking Confidence? You just finished a usability test. You had
