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From |
"Mark Hebblewhite" <mark.hebblewhite@ualberta.ca> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: conditional GLLAPRED in 3-level logit model |

Date |
Tue, 4 Oct 2005 22:53:38 -0600 |

Dear Stata list serve, I am writing to ask for advice about using GLLAPRED after GLLAMM to obtain conditional probabilities in a three-level (locations within individual wolves within wolf-packs) logit model with a random coefficient for an analysis I am doing on wolf resource selection. My model structure is : gllamm useavail (some other variables X1- - X3) disthgh, i( wolfuid packid) nrf(1,2) eqs(wolfhuman wolfhuman packhuman) fam(binom) link (logit) nip(8) trace where wolfhuman =1 and packhuman is set to be a random coefficient for var disthgh at the 3rd level (i.e. pack). So random intercepts for wolf and pack, and a random coefficient for disthgh at the packlevel. disthgh is a continuous variable describing distance to high human use trails and roads. My general question is how to obtain conditional predictions for the 3rd, or pack level, using GLLAPRED. I have acheieved this for a two-level model, but am running into conceptual problems for 3-level models. 1) At a general level, I am unclear how many generated variables I need to designate - do I need to specify GLLAPRED varname, u for all three levels of latent variables? i.e. GLLAPRED varname, u(var1 var2 var3) where var1 2 and 3 are defined by me as, and this leads to my second question, 2) How to determine what to set the value of the various random effects at. In my case, I have 5 wolf packs each with different mean distance to high human use (from 0.2km to 4.4km) - would it be reasonable to set these then representing the mean values for disthgh as the values at which to evaluate my conditional predictions at? This seems to be the case in one of the examples in the new stata book, but then elsewhere I get the impression its just set at values of SD's. So at a general level I am unclear it seems about GLLAPRED. I seem like I might be missing something quite basic here, but hopefully my question is not too trivial to obtain some advice. Gratefully yours, Mark Hebblewhite ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mark Hebblewhite, PhD Candidate Department of Biological Sciences University of Alberta Edmonton, Alberta T6G 2E9 Office phone: 1-780-492-0083 Home phone: 1-780-431-1476 email: mark.hebblewhite@ualberta.ca project website: http://ursus.biology.ualberta.ca/yhtelkwolfproject/ personal webpage: http://www.ualberta.ca/~mh12 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * * 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/

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