Quote:
Originally posted by DrGuile@Nov 1 2004, 11:10 AM
Isnt 2000 individuals a REALLY small population sample? How accuratly can it represents the different groups in the USA... (what's the US population now? 300mil?)
I know you can get pretty accurate with a moderate sized sample in modern statistical analysis, but that seems a bit of a stretch... eh, we'll see...
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Remarkably, the sampling error decreases very rapidly with the size of the sample. It is proportional to the square root of the sample size.
A truly random sample of 2000 will represent a population of 300 million to within the square root of 2000 or to within 2.2%.
In this case ...
1 standard deviation means the sample represents the total population to within 2.2% 67% of the time.
2 standard deviations means the sample represents the population to within 4.4% 95% of the time.
3 standard deviations means the sample represents the population to within 6.6% 99.7% of the time.