I am new to this contrast statement. Can you help me explain why the number should be  -5 -3 -1 1 3 5 not -4 -2 0 2 4?  ... View more

I don't know the answer to your question. Another article deals directly with your question (Statistics in Medicine 24:3089-3110). However, with PROC LIFETEST, you might consider the FREQ statement option, NOTRUNCATE, that prevents truncation on non-integer weights and the use of Wilcoxon scores (=n_i) instead of the default log-rank test scores (=1) so that these weights are incorporated in the estimation. ... View more

A plot of the standardized deviance residuals (STDRESDEV= option) or the likelihood residuals (RESLIK= option) can be useful. A plot of either against the predicted values should be randomly scattered about zero. Points beyond about 2 or -2 are not being fit well by the model. Plots of these residuals against the predictors can help you determine the proper form of the predictors in the model. Note the apparent overdispersion may really mean that you need additional effects in your model. If there is overdispersion, you could use the REPEATED statement to fit the model using GEE (even if you have no repeated data). GEE corrects for overdispersion. For more, see this usage note: http://support.sas.com/kb/22630 ... View more