Usability, Customer Experience & Statistics

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What is a Representative Sample Size for a Survey?

This common question mixes two concepts: representativeness and sample size. Representative samples mean asking the people in your population of interest. It is more important to ask a few of the right people what they think than a lot of the wrong people. Once you're talking to the right people you need to identify the highest margin of error you or the survey sponsor can tolerate then compute the sample size.

Read the Article

Featured Product: Survey Sample Size Package
Have you ever been asked how large a sample size you need for a survey? I put together a 23 page step-by-step guide and Excel calculator that will allow you to intelligently answer this common question. The guide and calculators:
  • Generate sample sizes for rating scale and binary response items
  • Contain a five-step process for finding the right sample size
  • Use industry defaults to estimate unknown standard deviations (a common problem for sample size estimates)
  • Contain four detailed examples and five practice exercises to help you understand the formulas and process
  • Show you how to find the right sample size for the popular Net Promoter Question and other Top-2 box questions
  • Provide confidence intervals around responses
See more about the Survey Sample Size Package.

If you've purchased the premium report "How to Conduct a Quantitative Usability Test" or the Quantitative Starter package get 15% off the Survey Sample Size Package until July 31st. Just login to your account to receive the discount.

Upcoming Event

I will be teaching a statistics tutorial this weekend with Jim Lewis at the Applied Human Factors and Ergonomics (AHFE) International Conference. If you're in Miami or at the conference be sure to send us a note.

Latest Measuring Usability Blog Entries

The Five Most Influential Papers in Usability
July 7, 2010
These five papers have had a large and lasting influence on the field of Usability and User Experience.

Want to Improve Usability? Count Calories
June 30, 2010
It is tempting to just find, fix and forget usability problems. It is tempting to skip one milkshake and think you're losing weight. Systematic measuring uncovers patterns and helps prevent major problems.

Five ways to make any usability test more credible
June 23, 2010
Whether you're conducting an early stage test of a prototype or late validation, these five tips can make any usability test more credible. The tips both temper skepticism about small samples and help you avoid overstating your findings.

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Jeff Sauro