Hobgoblin:

I think that in this case, (and John, correct me if I'm wrong), the "k-1" refers to what is called "between groups" degrees of freedom, while the "n-k" refers to "within groups" degrees of freedom. The within groups d.f. can be calculated by summing the "n-1" for all the groups, where "n" = the number of subjects in the group. It can also be done, as John stated it, by "n-k", where "n"= the TOTAL number of subjects in all the groups, and "k" = the number of groups. More than that, I don't know.