I'm reviewing a paper where the authors compare the survival of an insect fed on three different diets.
Following the survival analysis (using
Surv) they perform multiple comparisons of the mean survival among the treatments using the contrasts procedure from Crawley's The R book. They present their results a la a Tukey test (i.e., means with significantly different values have different letters).
Comparisons between 2 treatment levels in R can be done with
survdiff, but that generates a chi-square statistic which doesn't jive with what I'm seeing in the paper
The more general question of post-hoc tests in survival analysis when there are >2 treatment levels (akin to Tukey's test) has been asked on R-help before but never answered.
My problem is twofold: I'm not familiar with survival analysis to know if the contrast procedure is appropriate to the question, and I don't have access to Crawley's book.
Can someone provide an example of Crawey's method or point to a web resource where his method is explained?