I've originally made 48 GLM binomial models and compare the AIC values. But dispersion was very large: Example: Residual deviance: 8811.6 on 118 degrees of freedom I was suggested to do a quasibinomial afterwards but found that it did not help the dispersion factor of models and received a warning: Residual deviance: 3005.7 on 67 degrees of freedom AIC: NA Number of Fisher Scoring iterations: 13 Warning message: In summary.glm(qModel48.glm) : observations with zero weight not used for calculating dispersion 1) What does this warning message mean? 2) Is this quasibinomial step necessary or can I just compare the AIC of 48 glm models binomial even though dispersion is very large, well over 2. Jean -- View this message in context: http://r.789695.n4.nabble.com/GLM-Quasibinomial-48-models-tp4364137p4364137.html Sent from the R help mailing list archive at Nabble.com.