jsandber posted on Thursday, May 03, 2001 - 6:34 pm
Hi; I'm contemplating running a model as in the subject line, with either a latent class or other latent variable as the random effect(s) to capture heterogeneity. I was wondering if this was possible with Mplus, using a mixture of categorical and continuously measured covariates (this won't work with Jeroen Vermunt's LEM). I don't know how it would work, just hoping. Also, if estimating such a model is possible, is the user manual available for download so I can research how in more detail?
Yes, you can use Mplus Version 2 to do discrete-time survival analysis with a combination of categorical and continuous covariates. You can use a latent class variable to capture heterogeneity, while random effects (continuous latent variables) are not available in survival analysis with the current Mplus. The User's Guide has an example that shows how to do this. The User's Guide is not available for download. There is a forthcoming paper by Muthen & Masyn on this topic that I'd be happy to send as soon as I put the finishing touches on it.
Yes. It requires TYPE=MIXTURE MISSING and MISSING was not available for mixture models in Version 1.
David Bard posted on Sunday, June 18, 2006 - 2:22 am
I have a question related to identification of single-class discrete-time survival analyses. I was playing around with the examples in the manual using trial and error proof of principle to determine identification for various frailty specifications. I was a little confused and amazed that when I estimated an unstructured DTSA (i.e., unique thresholds for each DT variable) without covariates, estimation of a latent variance term appeared to be identified (provided I used threshold starting values that were correctly ordered and of reasonable magnitude). I should mention that while a replicable error variance did converge during estimation of this particular model, it was small and nonsignificant. However, my initial expectation was that the model would not converge at all. I've run some quick simulations and discovered this result is contingent on the presence of left censoring. Is this estimation of latent heterogeneity meaningful in this case or simply an artifact of the left censoring?
In a related question/concern, when left censoring occurs, the Pearson and Likelihood Chi-square values do not equal 0 when estimating the unstructured DTSA without covariates nor latent heterogeneity specified. Are these chi-square values interpretable/meaningful in this situation or should they be adjusted for this type of censoring?
I would like to do something very similar to example 3.9 random coefficient regression. Only difference is that Y is binary. But the s with y part doesn't work because they have to be continuous. Is a similar model with binary outcome possible?
I ran the model, but the integration points are 200, it gave me a fatal error message due to memory shortage.
On p.386, it says that integration points of 15 are already very heavy, so unfortunately, it seems that this model is not possible to run. I tried 1. "integration=montecarlo," 2. ignore the complex design of my survey data, 3. considerably reduce the sample size (I have 300,000 observations), and 4. reduce the number of variables to 3 as in the example, just to see if the model works, but none jointly or individually worked.
I know that 1 and 2 work individually, but 3, which is the combination of 1 and 2 doesn't work. I am not sure if I did wrong, or it is not possible to do it in mplus.
1. introduce random slope for x1 and residual covariance. CATEGORICAL IS u1; ANALYSIS: TYPE=RANDOM; MODEL: %within% s1 | u1 ON x1; f BY s@1 u1*; f@1;[f@0]; u1 ON x2 x3 z1 z2; s1 ON x3 z1;
2. introduce random slope for X3 and two-level structure WITHIN are x2 x3 x1; BETWEEN ARE z1 z2; CATEGORICAL IS u1; ANALYSIS: TYPE=TWOLEVEL RANDOM; MODEL: %within% u1 ON x1 x2; s2 | u1 ON x3; %between% u1 ON z1; s2 on z2;
3. 1&2 %within% s1 | u1 on x1; f by s1@1 u1*;f@1;[f@0]; u1 ON x2 x3; s1 ON x3; s2 | u1 on x3; %between% u1 ON z1; s1 ON z1; s2 ON z2;
Except X1 and Z2, all variables are dichotomous.
The error messages that I get from 3 are; 1.u1 is a within-level variable and cannot be used on the between level variables. 2.s1 is a between-level variable and cannot be used on the within-level variables. 3.The regression of u1 on X3 cannot be estimated because it defines random effect s2.
If I am understanding the description correctly, this should be a two-level discrete time survival. The person variance is on the within level and the school variance is on the between level. You can see how to setup discrete time survival in User's Guide example 6.19 but you will need to convert that into a two-level example.
But the main problem I think is still the fact that the basehazard model is independent of T. I don't think you want to have that. Like in discrete time survival you would want to have 5 thresholds - not one. So I would recommend using wide modeling like in 6.19
I think it will have to go to two-level models and you can still accommodate the cross classification but you will have to change the records that appear in two schools like this
1 1 0 1 1 1 0 2 1 2 0 3 1 2 1 4 1 2 . 5
would go to
u1 u2 u3 u4 u5 school
0 0 . . . 1 . . 0 1 . 2
and then but the model 6.19 (with free variance) on the between level.