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Date:         Fri, 23 Jul 2010 11:17:42 -0500
Reply-To:     Alex Reutter <areutter@us.ibm.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Alex Reutter <areutter@us.ibm.com>
Subject:      Re: Mixed model ANOVA degrees of freedom
In-Reply-To:  <AANLkTim2MLIntftGnU_eyHjDxt-6ILJhT3Jl8SOcMRfO@mail.gmail.com>
Content-Type: multipart/alternative;

The denominator df are computed using Satterthwaite's approximation. More details are in the MIXED algorithms documentation (Help > Algorithms).

Alex

From: Kambiz <ktavabi@googlemail.com> To: SPSSX-L@LISTSERV.UGA.EDU Date: 07/22/2010 06:33 PM Subject: Mixed model ANOVA degrees of freedom Sent by: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>

Typically when reporting test results from a GLM I use the format (F(df_factor_term,df_error_term)=F-stat, p=p-value), i.e., (F(n,n-1)=statistic,p=pvalue). My question is what is the equivalent format for a reporting results from a linear mixed model. For example if I have a fixed effect for term X SPSS outputs numerator and denominator degrees of freedom(df), I am assuming that F(df_numerator,df_denominator) is equivalent to F(df_factor_term,df_error_term), and in both instances the significance level for the F is from the F distribution with the degrees of freedom for the numerator and denominator mean squares. If that is correct, why does the denominator df in the mixed model not take on the value of n-1(or some constant, where n=number of factor levels)? Thanks in advance for your comments.

-- -K.


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