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Woodward Campus
What margin of error can you accept?
5% is a common choice
2008 Assessment Day Response Rate
5
%
The margin of error is the amount of error that you can tolerate. If 90% of respondents answer yes, while 10% answer no, you may be able to tolerate a larger amount of error than if the respondents are split 50-50 or 45-55. Lower margin of error requires a larger sample size. The confidence level is the amount of uncertainty you can tolerate. Suppose that you have 20 yesno questions in your survey. With a confidence level of 95%, you would expect that for one of the questions (1 in 20), the percentage of people who answer yes would be more than the margin of error away from the true answer. true The answer is the percentage you would get if you exhaustively interviewed everyone. Higher confidence level requires a larger sample size. How many people are there to choose your random sample from? The sample size doesn't change much for populations larger than 20,000.
What confidence level do you need?
Typical choices are 90%, 95%, or 99%
95
%
What is the population size?
If you don't know, use 20000
201
What is the response distribution?
Leave this as 50%
50
%
For each question, what do you expect the results will be? If the sample is skewed highly one way or the other, the population probably is, too. If you don't know, use 50%, which gives the largest sample size. This is the minimum recommended...