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From |
Maarten buis <maartenbuis@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Endless gradient-based optimization in multilevel mixed-effects linear regression model |

Date |
Wed, 11 Aug 2010 17:05:21 +0000 (GMT) |

--- On Wed, 11/8/10, Thiemann, Ulf wrote: > I am trying to run a multilevel mixed-effects linear > regression model using the xtmixed command. Age is one of > the covariates among others. <snip> However, the command > does not compute in some cases, if age is included. It usually helps to rescale variables such that the value zero falls within the range of the data. Remember, that the random effects models also model the constant, that is, the predicted value when all covariates are zero. You can imagine that Stata will find it easier to produce a model for that when that constant represents something that is not too far removed from your observations. Age is a usual suspect for such problems, as an age of 0 means newly born babies, which are often way outside the range of the data. Another common problem variable is year of birth. You can easily solve that by creating a new variable that contains age minus some reasonable constant, e.g. the age of the youngest observation or the average age in the first wave, and use that new variable instead of age. Hope this helps, 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: Endless gradient-based optimization in multilevel mixed-effects linear regression model***From:*"Thiemann, Ulf" <ulf.thiemann@kcl.ac.uk>

**References**:**st: Endless gradient-based optimization in multilevel mixed-effects linear regression model***From:*"Thiemann, Ulf" <ulf.thiemann@kcl.ac.uk>

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