Great question! If you don’t have a sample size calculator at the ready, we’ve got a handy-dandy table with the answers. To use the table, just ask yourself two questions:
How many people are in your population?
How representative do your survey results need to be?
Answering the first question is pretty simple. The second can be a bit trickier. Think of it this way–the closer your sample is in size to your population, the more representative your results are likely to be. And that’s why you’ll notice that the recommended sample size in the table below gets smaller as your tolerance for inaccuracy–or error–gets larger.
Let’s work through an example
Perhaps you’re interested in finding out how many people in your region of 10,000 people favor a longer school day for children and you’re willing to accept an error of plus or minus 5%. You sample 385 people, as the table recommends, and find that 70% of those surveyed are in favor of a longer school day. Given your 5% acceptable error rate, you can assume that if you’d asked every person in your region to take your survey, the actual proportion in favor of the longer school day would range from 65% to 75%.
But what if that range is too big? What if you need to be more precise? Well, then you’re going to need to sample more people. Using the table above and assuming a population size of 10,000 you can see that you would need 1000 survey respondents for a 3% error.
How many people should you invite to take your survey?
The table recommends the sample size you’ll need, not how many people you should invite to take your survey. So if you need 100 respondents and you expect that 25% of the people invited to take your survey will actually respond, then you need to invite 400 people (100 respondents ÷ .25 response rate = 400 invitations).
If you don’t know how many people are likely to respond to your survey invitation, it’s best to assume a fairly high response rate, like 25%, because it’s usually better to invite too few people than too many at first. You can usually invite more.
More to Come
We just covered a lot of information very quickly. If you’re interested in a better understanding of the terms we just referenced, watch for upcoming posts.
As always, we welcome your feedback, so let us know what you think in the comment section below.
P.S. If you are in need of people to take your survey, please click here to learn more about SurveyMonkey Audience—a new service that enables you to send your survey to respondents who match specific criteria you have in mind.
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