Large law departments should pay attention to how many of their lawyers leave, whether because the lawyers are asked to leave or because they choose to leave (See my post of Aug. 24, 2005 on the value of exit interviews.). That turnover rate is a basic measure of human capital management.
A more sophisticated analysis looks at how many lawyers leave who had top evaluations of performance as compared to those who left in the lower ranks of performance assessment. A law department might strive to keep the loss of high capability lawyers at something like 1 percent a year, while it tolerates the loss of lawyers with the lowest performance rankings at 20 percent or more a year (See my post of March 16, 2006 about A positions and A players.).