Coastal Services Center

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Determining Sample Size

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Sample size refers to the number of questionaires, interviews, surveys, etc. you will distribute or conduct during the needs assessment process. Having a large enough sample to prevent one sample from skewing the results is important. But, the size of your sample is not nearly as important as the proper design or the survey instruments. However, if there is bias in the data, it is unlikely to go away as you collect more data.

It is more important to obtain a representative sample than a large sample. Identify the groups you need and put more effort into getting a high response rate (e.g. by phoning, or sending reminders) rather than sending out huge numbers of questionnaires and letting a few undefined volunteers return them.

If you have the time, contacts and/or resources to be more rigorous about a sampling scheme, you might identify someone familiar with determining things like margin of error, degree of accuracy, standard deviation, mean degree of accuracy, etc. With pilot data in hand, a resource person with some experience could help you work out the total sample size you need for the kind of accuracy you choose.