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Mplus Discussion > Growth Modeling of Longitudinal Data >
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 Jonathan Codell posted on Thursday, February 07, 2013 - 2:24 pm
I have 12 data points (T1-T12) and would like to model for potential cubic growth in GMM. I managed to fit a decent linear and quadratic growth models but am unclear on to determine the appropriate times in the syntax for a cubic model:

i s | T1@0 T2@1 T3@2 T4@3.........T12@11

i s q | T1@0 T2@.01 T3@.04 T4@.09......T12@1.21

What would the appropriate syntax time be for a cubic model?

i s q cub | T1@? T2@?..........T12?

Thank you for your assistance.
 Linda K. Muthen posted on Thursday, February 07, 2013 - 2:31 pm
Yes, just add a fourth growth factor.
 Jonathan Codell posted on Thursday, February 07, 2013 - 2:46 pm
Thanks for the quick response. Can you clarify exactly what you mean though. As shown in my initial post I already have four growth factors listed (i s q cub) before the "|" symbol, but I am unclear on what I should list after the "@" symbol for each of the 12 time points. Thank you for your explanation.
 Linda K. Muthen posted on Thursday, February 07, 2013 - 3:48 pm
You list the linear time scores after the | symbol. I just noticed you did this incorrectly for the quadratic model. The time scores are always the linear and Mplus computes the others. Keep the on a small scale like 0 .1 .2 etc.
 Jonathan Codell posted on Thursday, February 07, 2013 - 11:33 pm
Thank you for the clarification. It looks like I was making this more complicated than needed. I really appreciate your help.
 Kiki van Broekhoven posted on Monday, July 03, 2017 - 11:16 pm
I have 7 data points and would like to investigate various forms of growth (linear, quadratic, cubic). I wondered what would be the best way to do this, that is: is there a specific order to introduce the various growth factors? So first try linear, than linear and quadratic, and so on? (and then check whether mean and variance of the growth factors are different from zero) Or should I be guided by other things?
 Kiki van Broekhoven posted on Friday, July 07, 2017 - 7:38 am
Could someone help me with this question? Thank you in advance.
 Bengt O. Muthen posted on Friday, July 07, 2017 - 4:35 pm
If theory can't guide you, yes, first try linear, than linear and quadratic, and so on and then check whether mean and variance of the growth factors are different from zero.
 Kiki van Broekhoven posted on Tuesday, July 25, 2017 - 3:25 am
Thank you for your reply. If I understand correctly, this could imply that e.g. a linear, quadratic AND cubic growth factor are needed when all of means and/or variances are different from zero?
 Bengt O. Muthen posted on Tuesday, July 25, 2017 - 5:19 pm
Right.
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