Survey Invitations, Sample Size &

Statistical Significance

You need to get enough completed surveys back so

that it accurately represents your population as a whole.

Here is a simple guide to calculate sample size and how many

people to send your survey to…

Population Size

Determine what your whole population size is.

Your population is the entire set of people you want to study with your survey.

Confidence Interval (margin of error)

Accuracy that responses received represents the views of population.

This will be your margin of error.

A standard confidence interval is 5% (up to 10%).

Confidence Level (accuracy)

How accurately your sample represents your population.

95% confidence level means you would get the same results 95% of the time even with different population samples.

Not advised to go below 90%.

Sample Size

Number of completed responses you need to get back.

Different from the number of people you need to invite.

Not everyone that you send your survey to will necessarily complete it.

Response Rate

Won’t know your response rate until after you send out your survey

Need to use a little bit of guesswork

Good recommendation would be to have a response rate estimate of 10-15% (conservative percentage)

So, how many people do you need to send your own survey to?

Sample Size ÷

Response Rate

For example,

A sample size of 200 and an estimated response rate of 10%, would be this calculation:

200 / 0.10 = 2000

In other words,

10% of 2000 = 200

Which is your required sample size.

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