alt Hacker NewsHi - please don't assume that retirements become job postings. Tenure lines have to be granted in many cases; if a dean is told by the provost to trim, then tenure lines are not granted after a retirement. My department has not matched its attrition rate for some time now.
I thought the 40% number seemed lower than my experiences suggest. But this is a solid point that suggests that even 84% is too low. I guess it could be as high as 90%.