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26 2011

How Many Respondents Do I Need?

Syndicated from: Bramm Research Blog

I am frequently asked by clients, “what sample size do we need”?  In a previous blog I redirected this question to focus on the importance of response rate.  But here I’m going to tackle the question of sample size. Recently I’ve discovered a handy table (Thank you Survey Monkey) for calculating the sample size required at three different error levels for various population sizes.  Okay, let me explain that last statement.  In a lot of survey research we are using a sample to make projections to a very large population e.g. all Canadian adults.  In this situation we can readily calculate a margin of error for different sample sizes.  However, when we’re dealing with a finite population e.g. members of an association, we need to use a slightly different formula to calculate the margin of error.  In a nutshell, when my total population decreases, the sample size required for a specific margin of error also decreases. The following link will take you to the aforementioned table.  This will be of benefit whether your association has 500 members or 100,000 members.

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