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Linear Mixed Models (LMM) in SPSS: Longitudinal and Nested Data

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IBM SPSS Academy 27 File Edit View Data Transform Analyze Graphs Utilities Mixed Models ▶ ▶ Linear Menü Yolu: Analyze → Mixed Models → Linear Yukarıdaki menü yolunu takip ederek analiz penceresini açın

📸 Linear Mixed Models menu path in SPSS

Why Use Linear Mixed Models?

Linear Mixed Models (LMM) handle data with complex dependency structures — repeated measurements on the same person, nested designs (students within classrooms), or longitudinal data with missing values. Unlike repeated measures ANOVA, LMM handles missing data via maximum likelihood estimation without listwise deletion.

Running LMM in SPSS

Step 1: Analyze → Mixed Models → Linear.
Step 2: Specify Subjects and Repeated: add the subject ID to Subjects, time variable to Repeated. Choose covariance type: Unstructured or AR(1).
Step 3: Add the DV to Dependent. Add fixed effects (treatment, time, interaction) to Fixed. Add random effects to Random if applicable.
Step 4: Academy: Parameter estimates, Tests for covariance parameters → OK.
SPSS Academy Output Viewer Tests of Fixed Effects (LMM) Source Num df F Sig. Intercept 1 4821.3 .000 Treatment 1 18.42 .000* Time 2 48.31 .000* Treatment × Time 2 12.47 .000* * p < .05 anlamlı sonuç gösterir

📸 LMM fixed effects table — significant interaction

APA Reporting

A linear mixed model with unstructured covariance revealed a significant Treatment × Time interaction, F(2, 182.4)=12.47, p<.001, indicating that treatment groups showed different trajectories of change over time.

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