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Old 05-01-2009, 11:01 AM   #24
Bobblehead
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Quote:
Originally Posted by peter12 View Post
Reliable data with confidence levels of 95% requires at least a sample of 1000. In fact, most academia requires confidence levels of 99%, requiring a sample size of 1500+. This sample means nothing.
The sample size you need will also affect your variance.

In this case, with this sample size you will have a 95% confidence level that the result is within +-5 (actually 5.34).

A sample size of 1000 gives you +-3 "19 times out of 20".

Handy calculator for this: http://www.surveysystem.com/sscalc.htm
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