Tenure:
9 year – 30% of the population, or 253 senior managers
10 year – 25%, or 211
11 year – 20%, or 169
12 year – 15%, or 126
13 year – 10% or 84
Let’s consider half of year 11 and all of year 12 and 13+ to be “in the pipeline”. That’s 295 senior managers competing for a given number of partner/principal/director (“partner”) spots.
http://goingconcern.com/2011/3/how-bad-are-the-odds-of-making-partner-at-a-big-4-firm