Questions about traj plug in

[Elyse Powell]

Hello,

I'm working through the examples on the traj plug in. I can get the ones posted to work just fine, but I'm having trouble understanding how the data needs to be coded so I can apply it to my own work. The general form of traj is

traj [ if exp ] , var( varlist ) indep( varlist ) model( string ) order( numlist )

So I'm trying to calculate trajectories for people buying something over time. So my var in varlist is the amount they bought at each time point {continuous, so buy1 is the amount purchased at timepoint1}, and my indep is this list of time points (years, coded as 1, 2, 3, so on). so my code looks like

traj, var( buy1 buy2 buy3 buy4) indep(year1 year2 year 3 year4) model( cnorm) order( 2 3 2) min(0) max (500)

what happens is that the program seems to be forcing the exact same number of people into each group (33% for each group) and can't calculate standard errors.

My data is in wide format, with a persons id being each observation.

If anyone has any insight into where my issue is I'd greatly appreciate it!

Elyse

[Roman Mostazir]

Problem can be of manifolds. Try with higher order polynomials with more number of groups. What is driving you to a three-group solution? 'Traj' modeling leads you to chose number of groups arbitrarily rather providing an objective solution, which again leads you to several trial and error steps. A better approach for group-based growth model is SITAR models ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3584986/ ), which I don't think anyone has written a program for Stata yet but there is program written on R.

[Giovanni Piumatti]

Hello,

when testing different class solutions, can I reasonably choose the model with the lowest AIC (or BIC) value? Are the values of AIC and BIC obtained in the traj output the correct ones or is there a postestimation command to obtaine them?

Thanks in advance!

Giovanni

[Amidu Raifu]

I just installed STATA 15.1 SE. After installation, I ran 'update all' command and I installed 'traj' plugin through this link

net from http://www.andrew.cmu.edu/user/bjones/traj
net install traj, force

However, whenever I run the Examples in 'traj' help window, the STATA program always shutdown without any results/outputs.

I have uninstalled the STATA several times but the problem still not solved.

I have contacted the author of the 'traj' plugin but he promised to have a look and get back to me.

STATA Suppport suggested to restart my computer and open the program in a safe mode but it does not work.

I would be glad if anyone has idea of the what is wrong.

Thank you,

Amidu

[Mark Chatfield]

Hi Amidu Raifu, do you have an update?
A colleague has the same issue.
I have an old version of the traj plugin, and it's not working now that I upgraded to Stata 15.1 SE.

[Chris Penfold]

I've just encountered this problem with the traj plugin after installing the '06 Jun 2018' update. I checked on a colleague's computer with a January 2018 update and the plugin worked fine. Is there a way of rolling back the incremental updates? Otherwise I'm going to try a fresh installation of Stata 15

[Mark Chatfield]

Hi Chris
I have a prior copy of traj and an old copy of Stata. If you can't match that, I don't think you'll find a solution this week. Someone should email Bobby L. Jones and see what he says.

[Chris Penfold]

I've got it working again - the problem was resolved by using the old version of Stata 15 (StataMP-64_old.exe) stored in the 'Stata15' folder. I plan to use this old version for analyses using the 'traj' plugin for the time being.

[Bobby Jones]

I have posted a fix. There was a problem with memory clean up that crept in with a recent update and only seemed to affect Stata 15. B.

[Amidu Raifu]

Thanks to Bobby Jones for fixing the problem and everyone who responded to the post.

[Nandita Krishnan]

Hello, I am having the same issue (I use Stata version 14). I am interested in looking at e-cigarette use trajectories using the following code:
traj , model(logit) var(ecig1-ecig4) indep(t1-t4) order(1)
But Stata immediately crashes when I run it. I am using Stata for Mac. Anyone else having the same issue or figured out a solution?

[Nandita Krishnan]

Is it possible to model linear splines using the traj plug-in?

[Bobby Jones]

You would have to code the linear spline as a time-varying covariate and use order 0 for the group.