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Date:         Sat, 9 Dec 2006 17:54:54 -0500
Reply-To:     Statisticsdoc <statisticsdoc@cox.net>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Statisticsdoc <statisticsdoc@cox.net>
Subject:      Re: guessing mean of bounded variable with 1:30 sampling ratio
Comments: To: nicola.baldini2@unibo.it
In-Reply-To:  <7.0.0.16.2.20061201115818.021fb5e0@unibo.it>
Content-Type: text/plain; charset="us-ascii"

Nicola,

Richard raises an important point about random sampling. Did you mean to say that the response rate was 400/12000 (as stated in the text of your message), or did you mean that the sampling ration was 400/12000 (i.e., n/N). If the former, random sampling seems highly unlikely. If the latter, random sampling is possible but should be documented (e.g., how were the samples drawn? Did the samples resemble the population in terms of other descriptive characteristics?).

HTH,

Stephen Brand

For personalized and professional consultation in statistics and research design, visit www.statisticsdoc.com

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]On Behalf Of Nicola Baldini Sent: Friday, December 08, 2006 6:11 AM To: SPSSX-L@LISTSERV.UGA.EDU 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. Nicola


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