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From |
"Leny Mathew" <lenymathewc@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: GLLAMM error: log-likelihood cannot be computed |

Date |
Mon, 8 Oct 2007 12:15:32 -0400 |

Hello, I'm trying to model the change of hormones over time on a group of 80 people. I have measurements at 3 points in time. The hormones have high variability at all the time points. Quite a few of them have undetectable values (set to 0) at all the time points. At time 1, almost 10% are undetectable, and this increases to almost 25% at the third time point. I used a GLM with gamma family and log link with a robust calculation of standard error to model the data. The model is significant for the time variable. Due to the high variability in the hormones, when I try to plot the fitted line (exponentiated) on to the scatter plot of the data, it is hardly visible. Is it correct to plot the "un-exponentiated" fitted line on a scatter plot with a log transformed Y-axis? Since I have used the GLM and not explicitly transformed the dependent variable, I'm not sure whether this is a correct way to go about it. Secondly, I tried to use create a random effects model as a better model for the above data. I used a random intercept and a random slope for the time variable. gen cons=1 eq inter: cons eq slope: time gllamm H_1 time, i(ID) nrf(2) nip(20) eqs(inter slope) family(gamma) link(log) adapt stata gave me an error that the log-likelihood cannot be computed. For this hormone I have another variable in which the undetectable values are set to a lower limit of detection. I tried running the above GLAMM model with that variable and stata was able to calculate the model. Why would this be the case? Any help is appreciated. Thanks, Leny * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**st: RE: GLLAMM error: log-likelihood cannot be computed***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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