How to Choose a Sample Size in Qualitative Research

Qualitative research is used to determine the reasons why people make decisions and behave the way they do. It's often employed by market researchers interested in understanding more about decision-making on a certain topic. When performing qualitative research, sample size is very important: If your sample is too small, you won't have a representative sample of the population as a whole. If the sample is too large, the information you receive might be unwieldy and the research can become very expensive. While qualitative research is an imperfect science, it does provide useful insights often neglected by quantitative research.

Instructions

1. Study the specific issue or topic you're planning to do qualitative research on and note any limitations that are immediately apparent. For example, if you are studying men over the age of 105, you know immediately that your sample size will probably be smaller than you'd like.

2. Determine the margin of error you're willing to accept. Within every research project, there will be "outliers," people whose answers are either false or are well beyond the statistical mean, or average. For example, if you were doing a study on coffee and you asked, "How many cups of coffee do you drink each week?", an answer of 500 would be an outlier that skews the rest of your data. The American Research Group offers a free calculator that helps you determine a margin of error for your project (see Resources) so you can easily determine the accuracy of your research based on sample size.

3. Perform qualitative research until you start hearing trends, the same types of responses over and over again. If you're talking about coffee and you've interviewed 15 people and 10 of them claim to drink between five and eight cups per week, that is clearly a trend. This may happen with as few as six participants or as many as 30. When in doubt, select a larger audience, since the more people you interview or survey, the greater the certainty that their responses reflect the population as a whole.

4. Stick to your budget. It doesn't matter how many participants you want to use if you can't afford it. Generally, the more participants, the greater the expense. Focus on completing research within your budget with the largest audience possible.

References

• OSRA: Organizational Research: Determining Appropriate Sample Size in Qualitative Research
• Social Research Methods: Sampling in Research
• Family Health International: Qualitative Research Methods Overview

Resources

• American Research Group: Margin of Error Calculator