Date:         Wed, 9 Oct 2002 18:09:38 -0500
Reply-To:     Jelani Mandara <jelani@citrus.ucr.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Jelani Mandara <jelani@citrus.ucr.edu>
Subject:      Re: Sample vs Population
Content-Type: text/plain; charset=windows-1252; format=flowed

Alison Neustrom wrote:

>What would you say if you had 80% of a non-random sample of a population (I
>sent them to everyone but only got back 80%)? Would you consider that a
>sample or a population?
>
>
>

Inferential stats rely on the size of the sample more than the % of the
population sampled.  This is a weakness, but since we rarely know the
actual size of the population, it's understandable.

So, I would argue that it depends on the size of the sample/population.
 If you have 80% of 100, then you may wish to increase alpha, since you
risk the chance of Type II errors (i.e., incorrectly concluding a null
result).  I think increasing alpha will be more reliable than just using
descriptives to test nulls in small samples when you have 80% of the
population.  In large samples (say, N > 1000) I doubt it matters.  Some
of the statisticians on the list may know for sure.

>-----Original Message-----
>From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]On Behalf Of
>Jelani Mandara
>Sent: Wednesday, October 09, 2002 11:50 AM
>To: SPSSX-L@LISTSERV.UGA.EDU
>Subject: Re: Sample vs Population
>
>
>Fink, Steven wrote:
>
>
>
>>Recently, I've been asked by several analysts about analyzing populations,
>>
>>
>that is, data not from a sample.
>
>
>>The purpose of a statistical test is to make estimates about the
>>
>>
>population.  If my data set IS the population, are significant tests
>appropriate?
>
>
>>
>>
>>
>No.  Descriptives and Effect Sizes are still relevant, but not
>inferential stats.
>
>
>
>>What about if my response rate (survey/unit) is low, say 20%.  For example,
>>
>>
>I sent surveys to everyone in the population, but only received 20% of
>responses.  Does this change your answer to the first question?
>
>
>>
>>
>>
>>
>
>Then you only have a (probably nonrandom) sample of the population.  The
>logic of inferential stats applies.
>
>
>
>>Thanks
>>
>>
>>
>>Steve
>>
>>
>>
>>
>>
>
>--
>Jelani Mandara
>Assistant Professor
>Human Development and Social Policy
>Northwestern University
>2120 Campus Drive
>Evanston, Il 60208
>
>Office Phone: (847)491-3122
>Web Page: http://www.sesp.northwestern.edu/people/sp/j_mandara.html
>
>
>

--
Jelani Mandara
Assistant Professor
Human Development and Social Policy
Northwestern University
2120 Campus Drive
Evanston, Il 60208

Office Phone: (847)491-3122
Web Page: http://www.sesp.northwestern.edu/people/sp/j_mandara.html