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 Lois Downey posted on Thursday, June 18, 2009 - 11:03 am
Before the release of Mplus 5.21, I ran a survival analysis that produced a loglikelihood of -292.574 and a parameter estimate of -.638 (p=.007) for my predictor of interest. With Mplus 5.21, the same model generates a loglikelihood of +6346.678 and a parameter estimate of -.102 (p=.173) for my predictor of interest.

Most other models that I have compared from before and after the Mplus 5.21 release look identical. The substantial change in this model may reflect the fact that I have a relatively small sample (n=488) and a reasonably large number of free parameters (17). Do you find the difference in results believable, and would you advocate accepting the Mplus 5.21 result?
 Lois Downey posted on Thursday, June 18, 2009 - 2:45 pm
As an amendment to my earlier posting, I would note that at least part of the problem may be the result of the fact that I have observations with survival time of 0. Do the two versions of 5.21 handle survival times of 0 differently?
 Linda K. Muthen posted on Thursday, June 18, 2009 - 3:07 pm
Please send the two outputs, your data, and your license number to support@statmodel.com.
 Michael posted on Wednesday, March 07, 2012 - 12:52 pm
I am attempting to use a discrete-time survival model to examine initiation of substance use.

I have a single, dichotomous outcome variable (substance use initiation), assessed at 5 time points. I would like to include both time-invariant (e.g., gender) and time-varying (e.g., stressful experiences) covariates, also assessed at the 5 time points. The central question I am interested in is whether recent stressful experiences represent a risk factor for substance use initiation.

Following are the VARIABLE and MODEL statements I am working with.

VARIABLES ARE
SUW1-SUW5 !Substance use initiation, coded 0 (no), 1 (yes), and 999 (missing or yes at a previous wave)
Gender !coded 0 = female, 1 = male
STW1-STW4 !Past year stressful experiences (continuous)

MODEL:
f by SUW1@1 SUW2@2 SUW3@3 SUW4@4 SUW5@5;
f@0;
f on Gender;
SUW2 on STW1 (A);
SUW3 on STW2 (A);
SUW4 on STW3 (A);
SUW5 on STW4 (A);

Have I included the time-varying covariates correctly? I constrained them to be equal across the waves, as it does not seem necessary to unconstrain them for what I am doing.

Your feedback is greatly appreciated.
 Linda K. Muthen posted on Thursday, March 08, 2012 - 12:37 pm
It looks like you are using the time-varying covariate correctly but I wonder about your BY statement. It should be

f by SUW1-SUW5@1;

See Example 6.20 in the user's guide.
 Michael posted on Thursday, March 08, 2012 - 3:44 pm
Thank you for your response. The @1-5 was an error from reducing the statement to post here. I was thinking survival, but it seems that my fingers liked growth better. Thanks again.
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