Isn’t one difference that the genlinmixed model uses an unstructured cov matrix while the glm model uses the standard repeated measures assumption of compound symmetry? What happens if you impose a compound symmetry cov matrix on the genlinmixed model?
Gene Maguin
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of Kornbrot, Diana
Sent: Wednesday, March 01, 2017 4:56 AM
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[hidden email]Subject: comparing GeneraliZed linear MIXED (GLMM) with GLM REPEATED
Hi
One might expect (hope) these procedures would have same results when GLMM has normal with identity link and some settings.
NOT SO.
Design. this is complex as want to test limits, between factors are very unbalanced subject variable has n = 87
Factor 1, between: betwennrepeat, 2 level
Factor 2, between: Nlevels, 4 levels
Factor 3, repeated: analysis, 5 levels
Nearest I can get is below with following syntax
GLM repeated
GLM raw_f lgt_f z_f FlogitVC_f FprobitVC_f BY bewennrepeat Nlevels
/WSFACTOR=analysis 5 Repeated
/CONTRAST(Nlevels)=Repeated
/METHOD=SSTYPE(3)
/EMMEANS=TABLES(OVERALL)
/EMMEANS=TABLES(bewennrepeat)
/EMMEANS=TABLES(Nlevels)
/EMMEANS=TABLES(analysis)
/EMMEANS=TABLES(bewennrepeat*Nlevels)
/EMMEANS=TABLES(bewennrepeat*analysis)
/EMMEANS=TABLES(Nlevels*analysis)
/EMMEANS=TABLES(bewennrepeat*Nlevels*analysis)
/PRINT=DESCRIPTIVE ETASQ HOMOGENEITY
/CRITERIA=ALPHA(.05)
/WSDESIGN=analysis
/DESIGN=bewennrepeat Nlevels bewennrepeat*Nlevels.
GLMM
*Generalized Linear Mixed Models.Key settings in bold
GENLINMIXED
/DATA_STRUCTURE SUBJECTS=id REPEATED_MEASURES=analysis COVARIANCE_TYPE=UNSTRUCTURED
/FIELDS TARGET=trans1 TRIALS=NONE OFFSET=NONE
/TARGET_OPTIONS DISTRIBUTION=NORMAL LINK=IDENTITY
/FIXED EFFECTS=analysis bewennrepeat Nlevels analysis*bewennrepeat analysis*Nlevels bewennrepeat*Nlevels analysis*bewennrepeat*Nlevels USE_INTERCEPT=TRUE
/BUILD_OPTIONS TARGET_CATEGORY_ORDER=ASCENDING INPUTS_CATEGORY_ORDER=ASCENDING MAX_ITERATIONS=100 CONFIDENCE_LEVEL=95 DF_METHOD=SATTERTHWAITE COVB=MODEL PCONVERGE=0.000001(ABSOLUTE) SCORING=0 SINGULAR=0.000000000001
/EMMEANS TABLES=analysis COMPARE=analysis CONTRAST=PAIRWISE
/EMMEANS TABLES=bewennrepeat CONTRAST=NONE
/EMMEANS TABLES=Nlevels COMPARE=Nlevels CONTRAST=PAIRWISE
/EMMEANS TABLES=analysis*bewennrepeat COMPARE=analysis CONTRAST=PAIRWISE
/EMMEANS TABLES=analysis*Nlevels COMPARE=analysis CONTRAST=PAIRWISE
/EMMEANS TABLES=bewennrepeat*Nlevels COMPARE=bewennrepeat CONTRAST=PAIRWISE
/EMMEANS TABLES=analysis*bewennrepeat*Nlevels COMPARE=analysis CONTRAST=PAIRWISE
/EMMEANS_OPTIONS SCALE=ORIGINAL PADJUST=LSD.
Results.
For GLM repeated have only included Roy’s largest root,as this is nearest to GLMM
Note on df
For between factors there are 7 =(4-1 for Nlevels) + (2-1 for bewennrepeat) +1 for grand mean
For GGLMM: df2 = 80 for all F tests
For repeated Roy’s: between factors still have df2 = 80
Repeated factors have lower df,as the related measures df are also taken into account
Comparison
GLMM unnstructured
satterthwaite
model
Multivariate Tests
Roy's largest root
Source
F
df1
df2
Sig.
Effect
F
df1
Error df
Sig.
analysis
6.52
4
80
.000136
analysis
6.27
4
77
.000201
bewennrepeat
21.04
1
80
.000016
bewennrepeat
21.04
1
80
.000016
Nlevels
.10
3
80
.962591
Nlevels
.10
3
80
.962591
analysis * bewennrepeat
7.79
4
80
.000024
analysis * bewennrepeat
7.49
4
77
.000038
analysis * Nlevels
.76
12
80
.688855
analysis * Nlevels
1.76
4
79
.145261
bewennrepeat * Nlevels
.25
2
80
.783290
bewennrepeat * Nlevels
.25
3
80
.864661
The results are identical for between factors,
BUT slightly different for repeated factor
WHY?, WHICH RESULTS are to be recommended?
best
Diana
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