Date: Sat, 9 Dec 2006 10:41:03 -0500
Reply-To: Statisticsdoc <email@example.com>
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From: Statisticsdoc <firstname.lastname@example.org>
Subject: Re: guessing mean of bounded variable with 1:30 sampling ratio
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You have the Central Limit Theorem working for you here. Even though the
distribution of individual cases is not normal, the distribution of sample
means (with a sample size of 400) will approximate the normal distribution
and should provide you with a reasonable estimate of the population mean and
the standard error of the means of samples of 400 cases.
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From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]On Behalf Of
Sent: Friday, December 08, 2006 6:11 AM
Subject: guessing mean of bounded variable with 1:30 sampling ratio
I have a population of N=12000. I want to know the mean (and possibly the
standard deviation) of a variable x, bounded between 1 and 7. I took a
(let's suppose random) sample of n=400 and estimated mean = 3.14 (standard
error = .15) and standard deviation = 2.28. The sample strongly departs from
normality. Can I trust such estimates? How much? Can I attach a p-value to
them? I need to state formally that, despite a ridicolous response rate, my
research is not that bad.