Posted by
Zdaniuk, Bozena-3 on
Mar 16, 2021; 8:16pm
URL: http://spssx-discussion.165.s1.nabble.com/Interpretation-of-interaction-with-time-varying-predictor-Growth-model-tp5740294p5740315.html
Hi Oliver,
You can just recode your time points so that time 0 has the highest numerical value, e.g., time 0 has a value of 4, time 1 =3, time 2=2 , time 3=1 and time 4=0.
You just have to remember to take the intercept from the first model before recoding the time if you report it.
Cheers
b
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Sent: March 16, 2021 1:11 PM
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Subject: Re: Interpretation of interaction with time-varying predictor (Growth model)
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Bozena,
Thanks for your input. I agree with you that the "estimates of fixed effects" box from the SPSS output file will generate interaction terms with p-values across all levels, but the problem is the "Reference category" that SPSS uses by default. My understanding is that SPSS uses the highest category as the reference, which may not be enough and relevant. In my output, I see that the interaction is significant when comparing Time1 versus Time4, but I'm particularly interesting in examining what happens with the interaction when Time0 (baseline) is used as the reference category.
Is there any way to change the reference category ? This way, it would solve the problem and perhaps avoid the need to rely on planned interaction contrasts.
Thanks again everyone.
O.
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http://spssx-discussion.1045642.n5.nabble.com/file/t340718/Interaction%3B_output.jpg>
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