Improving the Prediction of the Number of Usability Problems

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

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The UX of Vacation Rental Websites

The COVID-19 pandemic has led to significant changes in how people have vacationed in 2020. To get away from it all without spending time in crowded places, vacationers have turned to vacation rental websites and have planned longer stays. For example, Airbnb recently reported a year-to-year doubling of long-term (>28 days) rentals and a shift

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What Do You Gain from Larger-Sample Usability Tests?

We typically recommend small sample sizes (5–10) for conducting iterative usability testing meant to find and fix problems (formative evaluations). For benchmark or comparative studies, where the focus is on detecting differences or estimating population parameters (summative evaluations), we recommend using larger sample sizes (20–100+). Usability testing can be used to uncover problems and assess the

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Sample Size Recommendations for Benchmark Studies

One of the primary goals of measuring the user experience is to see whether design efforts actually make a quantifiable difference over time. A regular benchmark study is a great way to institutionalize the idea of quantifiable differences. Benchmarks are most effective when done at regular intervals (e.g., quarterly or yearly) or after significant design

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Sample Size in Usability Studies: How Well Does the Math Match Reality?

We’ve written extensively about how to determine the right sample size for UX studies. There isn’t one sample size that will work for all studies. The optimal sample size is based on the type of study, which can be classified into three groups: Comparison studies: Comparing metrics for statistical differences Standalone studies: Estimates a population

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Getting Started Finding the Right Sample Size

Most methods in UX rely on collecting data (behavioral and attitudinal) from a sample of participants. But knowing how many participants you should use is not a simple question. What’s particularly difficult about learning how to compute the right sample size for a study is that books and articles can get overly technical; it’s hard

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How to Find the Sample Size for 8 Common Research Designs

What sample size do we need? It’s consistently among the most common questions I get from researchers. It can be a confusing process, but that’s why we cover sample-size planning at the Denver UX Boot Camp. Determining the right sample size for a project is a science–an imprecise science. It’s like appraising a house: you

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Is Observing One User Worse Than Observing None?

Seeing is believing. Observing just a handful of users interact with a product can be more influential than reading pages of a professionally done report or polished presentation. But what if a stakeholder only has time to watch two or just one of the users in a usability study? Are there circumstances where watching some

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5 Reasons You Should and Should Not Test With 5 Users

There are a lot of misconceptions about when it is and when it is not appropriate to test with five users. There’s no reason to take an extreme position on this issue and think it’s never acceptable or always the right number. Instead you should understand what you can and cannot learn from just a

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