Hi I am performing a lmer on count data with several explanatory variables both continuous and categorical. All go in fine apart from two of the continuous variables that have na's in them. They give errors like: Leading minor of order 5 in downdated X'X is not positive definite I used the as.factor function to define my categorical factors as categorical but when i ask is.factor about my two continuous variables that i didnt use the as.factor for it replies yes. I have so far come to conclusion that because the data contains na's R is automatically reading it as categorical not continuous and i was wondering if there is a way to overcome this? Thanks Tonker ps i do use the na.action=na.omit in my model so if possible i would like to not have to delete all the records with na in in these two explanatory factors. -- View this message in context: http://www.nabble.com/na%27s-and-continuous-variables-tf4792738.html#a13710596 Sent from the R help mailing list archive at Nabble.com.