Message/Author 

Gareth posted on Monday, January 19, 2009  8:35 am



In growth mixture modeling, could the KNOWNCLASS option be used to specify a class of people who scored zero on the outcome for every time point? 


No. Instead set the thresholds in one class to +15. In that class, also fix the means and variances of the growth factors to zero. 

Gareth posted on Wednesday, January 21, 2009  2:38 am



The outcome variable is continuous, not categorical. Should I therefore fix the mean to 0 and the variance to 0 for y1y3, in class 1? 

Gareth posted on Wednesday, January 21, 2009  2:42 am



The outcome variable is continuous, not categorical. Should I therefore fix the mean to 0 and the variance to 0 for y1y3, in class 1? %c#1% [y1y3@0]; [i@0 s@0]; s@0 i@0; 


This approach does not work with a continuous outcome. You might instead consider twopart modeling. See Example 6.16 in the Mplus User's Guide. 

Gareth posted on Saturday, January 24, 2009  5:33 am



I have modified example 6.16, but is the floor variable treated as a latent class in its own right (so I should ask for classes=5), or is it present throughout, in the overall model (so I should ask for classes=4). I anticipate four latent classes (increasing, decreasing, rapidly increasing, consistently low), in addition to the "floor" variable (no use)? Ideally, I want to compare the four growth patterns to "no use". If this is not possible, I can use the consistently low class instead, but I would like to know how the zeros are accounted for in twopart mixture growth models. CLASSES = c (4)! MODEL: %overall% iu su  bin1@0 bin2@1 bin3@2; iy sy  cont1@0 cont2@1 cont3@2; iy sy ON x; su@0; iu WITH sy@0; 


Twopart modeling does not involve a class per se. So if you hypothesize 4 classes, then classes = c(4); Only if you also hypothesize a class of zero (floor value) throughout would you specify a zero class for the u part; but that you have to add yourself. 

Gareth posted on Monday, January 26, 2009  9:39 am



I hypothesize a class of zero throughout, so I have attempted to add a zero class for c#1. I am expected the other four classes to show different growth patterns, but a zero value for the first class throughout. Is this the correct syntax? CLASSES = c (5); MODEL: %overall% iy sy  cont1@0 cont2@1 cont3@2; iu su  bin1@0 bin2@1 bin3@2; iy sy ON x; %c#1% iy sy  cont1@0 cont2@1 cont3@2; iu su  bin1@0 bin2@1 bin3@2; su@0; iu WITH sy@0; 


No, you should say %c#1% iusu@0; [iusu@0]; [bin1$1bin3$1@15];  check in the Mplus plot that this gives you a zero class. 

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