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I have a small dataset (N = 60, 2 groups) on which I would like a Mixed Model (or alternative) analysis, using SPSS, done.
I have experience with Repeated Measures ANOVAs but in this particular case, the dataset has unequal numbers of observations over time, as measurements took place only until participants were done performing a specific task. A traditional Repeated Measures ANOVA would kick out most cases, due to missing values. I have maximally 6 observations per subject -- ALL subjects have data for the first observation, more than 40 have data for the second observation, 30 have the first three datapoints, 17 have 4, and 10 have all six datapoints. I would like to compare the two groups, with the six observations as within-subjects variable. I can provide the data, of course, but in addition to the output of the analysis, would like a SPSS Syntax file that explains the procedure (or at least in as simple as possible terms the steps/ingredients of the syntax -- I understand ANOVA syntax but have never done a Mixed Model in SPSS), so I can run variations on this analysis myself in the future.
N.B.: I am assuming that SPSS Mixed Models are the way to go and would like to have the analysis done for the following reason: More descriptive analyses suggest that the two groups do not differ at the start, but that they DO differ towards the end -- but the thing is that at that point we are dealing with a subgroup, as most subjects will have completed the task at an earlier point and we do not have the last few observations for them.
If there are other ways to analyze (survival analysis? Would that allow me to conclude about different (sub)groups? I would have to have that explained to me though) this, I would be interested in hearing more about it.