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 Linear mixed model issues

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Emanuel Festino posted Mon August 18, 2025 03:09 AM

Hi all,
I’m currently working on a dataset and struggling to properly set up a repeated-measures linear mixed model in SPSS, and I would greatly appreciate your guidance.


In my study, the dependent variable is jump performance. Each participant has four repeated measurements, resulting from a combination of two factors:
• Time: pre and post intervention
• Leg: dominant and non-dominant

So for each subject, I have:
• pre-dominant
• pre-non-dominant
• post-dominant
• post-non-dominant

These conditions are stored in two separate columns: one indicating the leg (dominant vs. non-dominant) and one for time (pre vs. post). My aim is to evaluate whether a specific type of training intervention had an effect on jump performance, considering both leg and time as repeated factors. The variable "codice" is the code (so the subjects). When i insert subjcet as random effect, with intercept i have problem. The output say: 

The final Hessian matrix is not positive definite although all convergence criteria are satisfied. The MIXED procedure continues despite this warning. Validity of subsequent results cannot be ascertained.

This is the syntax

MIXED HOPPING BY DOM0NODOM1 PRE0POST1
/CRITERIA=DFMETHOD(RESIDUAL) CIN(95) MXITER(100) MXSTEP(10) SCORING(1) SINGULAR(0.000000000001)
HCONVERGE(0.00000001, RELATIVE) LCONVERGE(0, ABSOLUTE) PCONVERGE(0, ABSOLUTE)
/FIXED=DOM0NODOM1 PRE0POST1 DOM0NODOM1*PRE0POST1 | SSTYPE(3)
/METHOD=REML
/PRINT=SOLUTION TESTCOV
/RANDOM=INTERCEPT | SUBJECT(CODICE) COVTYPE(VC)
/REPEATED=DOM0NODOM1*PRE0POST1 | SUBJECT(CODICE) COVTYPE(CS)
/EMMEANS=TABLES(DOM0NODOM1) COMPARE ADJ(BONFERRONI)
/EMMEANS=TABLES(PRE0POST1) COMPARE ADJ(BONFERRONI)
/EMMEANS=TABLES(DOM0NODOM1*PRE0POST1) .



Could someone help me please?