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From |
Maarten Buis <maartenlbuis@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Fw: appling a gamma distribution random effects model. SAS to Stata |

Date |
Wed, 7 Dec 2011 11:46:45 +0100 |

On Wed, Dec 7, 2011 at 10:31 AM, Brent McSharry wrote: > I have some SAS code to apply a model to patient data, and I would like to > apply this to our local data (the model is externally validated to predict > length of ICU stay in days). > Unfortunately I have no idea about SAS syntax, and exclusively use stata. > > the first part of the SAS code obviously generates a linear coefficient & > applies an exp link > ie in Stata: > > scalar s2u = 1 > scalar a = 2 > generate linCoef = 0.2 + varA * 0.4 + varB*-0.02 ... > generate mu= exp(linCoef) > gen b = mu/a > > and then i am affraid I am lost (particularly as the = signs stop and the > tildas ~ begin) > > model los_days ~ gamma(a,b); > random u ~ normal(0,s2u) subject=varY out=random; > predict mu out=predout; > run; I have no idea about the syntax in Some Alternative Software either, but the tilde is often used for "distributed as", which makes sense in your case. I guess you want to create a random variables from that validated model. Now you need to figure out where exactly the random term enters the model. I guess it is added to the linear predictor, but you need to check that in the documentation of that model. You also need to check the exact parameterization of the gamma distribution used in that model and possibly translate that to the parameterization used in -rgamma()-. After that it will be a couple of -generate- commands calling the -normal()- and -rgamma()- functions, see -help random_number_functions-. I know that this is not a lot, but I hope this gets you started, Maarten -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl -------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: Fw: appling a gamma distribution random effects model. SAS to Stata***From:*Nick Cox <n.j.cox@durham.ac.uk>

**References**:**st: Fw: appling a gamma distribution random effects model. SAS to Stata***From:*"Brent McSharry" <brent@focused-light.net>

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