<p>Right on arabrab! But let me add . . . even if your advisor has tenure, it doesn’t mean he or she will stay at your school. It happened to me! I was too far along to go with him (he took his younger students with him to the new place). Very much slowed me down.</p>
<p>In History (my field) several years ago a study was conducted and came up with average time to degree being 12 years! I think that’s not completely accurate (I think it’s shorter at the “better” places where students pretty much do history full time) but in my cohort at an ivy, the fastest to finish was 7 years and most of us were in the 8-9 year range. And many did not get jobs (1990s horrifyingly bad job market!)</p>