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Unformatted text preview: I OWA S TATE U NIVERSITY Department of Animal Science I OWA S TATE U NIVERSITY Department of Animal Science PROC GLIMMIX Generalized Mixed Linear Models Animal Science 500 Lecture No. 17 18 October 25, 2010 I OWA S TATE U NIVERSITY Department of Animal Science GLIMMIX Information ◆ PROC GLIMMIX is a procedure for fitting G eneralized Li near Mix ed M odels ◆ GLiM’s (or GLM’s) allow for nonnormal data and random effects ◆ GLiM’s allow for correlation amongst responses An Introduction to Generalized Linear Mixed Models Using SAS PROC GLIMMIX P. Gibbs, SAS Technical Support I OWA S TATE U NIVERSITY Department of Animal Science Getting GLIMMIX ◆ SAS 9.1 Download addon (Windows, Unix, Linux) from ■ http://support.sas.com ■ http://www.sas.com/statistics ◆ Supported on a limited number of platforms and platform configurations ◆ SAS 9.2 (available now for most academic sites) An Introduction to Generalized Linear Mixed Models Using SAS PROC GLIMMIX P. Gibbs, SAS Technical Support I OWA S TATE U NIVERSITY Department of Animal Science GLIMMIX overview ◆ PROC GLIMMIX fits statistical models to data with correlations or nonconstant variability and where the response is not necessarily normally distributed. ◆ These models are known as generalized linear mixed models (GLMM). ◆ The GLMMs, like linear mixed models, assume normal (Gaussian) random effects. ◆ Conditional on these random effects, I OWA S TATE U NIVERSITY Department of Animal Science GLIMMIX overview ◆ The exponential family comprises many of the elementary discrete and continuous distributions and include: ■ Binary, ● The experiment consists of n repeated trials. ● Each trial can result in just two possible outcomes. We call one of these outcomes a success and the other, a failure. ● The probability of success, denoted by P , is the same on every trial. ● The trials are independent  that is, the outcome on one trial does not affect the outcome on other trials. ■ Binomial, I OWA S TATE U NIVERSITY Department of Animal Science GLIMMIX overview ◆ The exponential family comprises many of the elementary discrete and continuous distributions and include: ■ Binomial, ● Situations in which the coin for example is biased, so that heads and tails have different probabilities. ● The probability distributions for which there are just two possible outcomes with fixed probability summing to one. ● These distributions are called are called binomial distributions ■ Poisson, and ■ Negative binomial distributions, I OWA S TATE U NIVERSITY Department of Animal Science GLIMMIX overview ◆ The exponential family comprises many of the elementary discrete and continuous distributions and include: ■ Poisson, ■ The poisson distribution is an appropriate model for count data....
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 Fall '09

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