1
$\begingroup$

In my experiment I measure accuracy (0-1) in two groups, on two different types of stimuli. I use the generalized linear mixed model because I think this is the only model that can deal with binary DVs and with nested data (trials within the same participant).

SPSS syntax:

GENLINMIXED
  /DATA_STRUCTURE SUBJECTS=id REPEATED_MEASURES=trial COVARIANCE_TYPE=AR1
  /FIELDS TARGET=accuracy TRIALS=NONE OFFSET=NONE
  /TARGET_OPTIONS DISTRIBUTION=BINOMIAL LINK=LOGIT
  /FIXED  EFFECTS=group stimulusfactorA stimulusfactorB group*stimulusfactorA group*stimulusfactorBstimulusfactorA*stimulusfactorBgroup*stimulusfactorA*stimulusfactorB USE_INTERCEPT=TRUE
  /RANDOM USE_INTERCEPT=TRUE COVARIANCE_TYPE=VARIANCE_COMPONENTS
  /BUILD_OPTIONS TARGET_CATEGORY_ORDER=ASCENDING INPUTS_CATEGORY_ORDER=ASCENDING MAX_ITERATIONS=100 CONFIDENCE_LEVEL=95 DF_METHOD=RESIDUAL COVB=MODEL
  /EMMEANS_OPTIONS SCALE=ORIGINAL PADJUST=LSD
  /SAVE PREDICTED_VALUES(PredictedValuere)  PREDICTED_PROBABILITY(PredictedProbabilityre) MAX_CATEGORIES(25) CONFIDENCE(Confidence1re) CONFIDENCE_METHOD(PREDICTEDPROBABILITY) CONFIDENCE_INTERVALS(CIre) PEARSON_RESIDUALS(PearsonResidual1re).

In the fixed effect table with the F-tests, I see a very large effect of Stimulusfactor B (which has 4 categories). However, when I look at the simple contrasts, I see no significant effects at all. The graphs don't show the P-value, but just a red line (instead of a gold one), indicating that it is not significant. I feel something is wrong with this model but I am not sure what it is. Can someone help out?

PS When I analyze the averages per condition (percentages correct) in a simple repeated measures ANOVA, the pairwise comparisons do show significant differences.

$\endgroup$
  • 4
    $\begingroup$ I know that genlinmixed only reluctantly gives tables of parameter estimates and their standard errors, but you could possibly get that information for us? It is almost impossible to answer as is, I think. If you are at all familiar with other statistical packages (e.g., R, SAS, Stata) I would encourage you to try one of those. The syntax for this type of model is much easier, and you get standard output that can be readily shared rather than "a red line instead of a gold one". $\endgroup$ – Joshua Jul 18 '12 at 2:12
  • $\begingroup$ What's your sample size? What are these efffects? How well are they estimated? $\endgroup$ – Peter Flom - Reinstate Monica Nov 24 '17 at 13:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.