Date: Wed, 19 Feb 1997 10:42:48 0600
ReplyTo: "Nichols, David" <nichols@SPSS.COM>
Sender: "SPSSX(r) Discussion" <SPSSXL@UGA.CC.UGA.EDU>
From: "Nichols, David" <nichols@SPSS.COM>
Subject: Re: Posthoc query
>
>From: William B. Ware[SMTP:wbware@EMAIL.UNC.EDU]
>Sent: Wednesday, February 19, 1997 6:15 AM
>To: Multiple recipients of list SPSSXL
>Subject: Re: Posthoc query
>
>On Thu, 20 Feb 1997, John Reece wrote:
>
>> A simple query: Is the Tukey B posthoc test the same as the posthoc test
>> often called the TukeyKramer? If _not_, then what is the preferred method
>> for analysing posthoc when sample sizes are unequal (sometimes wildly)?
>> Does it involve taking a harmonc mean of all groups?
>
>The Tukey B procedure is a compromise between the Tukey A procedure and
>the studentized NewmanKeuls procedure... The Tukey A uses the same
>critical value for each pairwise contrast, no matter how many means are in
>the "range." The SNK is based on a "layered" approach, where the critical
>value varies with the number of means in the range. The Tukey B procedure
>uses the average of Tukey B and SNK. For example, consider the
>"manufactured" example below...
>
>#means in range 2 3 4
>
>Tukey A 4 4 4
>
>SNK 4 5 6
>
>Tukey B 4 4.5 5.0
>
>**********
>
>In my opinion, the most appropriate is Tukey A. As for the TukeyKramer,
>it is a modification of the Tukey A. It uses the harmonic mean of the
>samples sizes of the two groups being contrasted, rather than the harmonic
>mean of all sample sizes. It is the default in SPSS when you run Tukey's
>A.
>
>
>_____________________________________________________________________________
>_
>
>William B. Ware, Professor and Chair Educational Psychology
>CB# 3500 EMAIL:
>wbware@unc.edu
>University of North Carolina PHONE:
>(919)9665266
>Chapel Hill, NC 275993500 FAX:
>(919)9621533
>
>URL:http://www.unc.edu/~wbware/
>_____________________________________________________________________________
>_
Bill's explanation is accurate. To elaborate, the default method in
pre7.x
releases of SPSS, using the individual cell sizes or their harmonic mean
rather
than the harmonic mean of all cell sizes, is also known as the
TukeyKramer
method, and it is to be generally recommended in opposition to other
variants
on Tukey methods. What Bill refers to here as Tukey A is sometimes
called Tukey's
HSD (Honestly Significant Difference), and I think we refer to it that
way in
some of our documentation. In Release 7.0 and above, we actually give
two forms
of results for the Tukey approach. One does all pairwise comparisons
using the
Tukey A/HSD or TukeyKramer approach for unequal N, while the other
gives
homogeneous subsets based on the harmonic mean approach. For the TukeyB
option,
we give only the homogeneous subsets results, since the test is by
definition a
sequential test.
David Nichols
Senior Support Statistician
SPSS Inc.
nichols@spss.com
