<p>There's always some lateral movement and losses of senior people to retirement, but in general there's less movement in the departmental rankings than you might suppose. There are powerful institutional reasons for this. When the strongest departments lose good people, they're usually able to replace them with good people. Schools want very badly to maintain and build on existing strengths, so if they lose good people in a strong department, that department will usually have the resources it needs to make strong replacement hires, and they'll be looking for the best they can get. On the supply side, the best new entrants into the field and the best people on less prestigious faculties elsewhere will most strongly covet those slots on faculties with existing strong reputations. So the strong tend to stay strong, unless the faculty just blows up and people depart en masse, which does happen---though it's rare. By the same token, it's very difficult for a school to come from nowhere and break into the top ranks; more commonly, there's slow incremental movement, and a rise to the top is a decades-long quest. But of course, there is the occasional exception. </p>
<p>It's also true, of course, that the smaller the department the greater will be the impact of a small number of departures. But even in a field like Classics, the top schools have quite large faculties. Michigan, for example, lists 24 people at the professor, associate professor, or assistant professor levels in its Classics department. In a department that large and that prestigious, the loss of one or two very good people will be felt temporarily, but it won't throw the whole department out of whack---they'll be easily replaced with very talented and very eager newcomers. At LACs it's different. If you've got 5 or 6 people in the department and two leave, you could go from having a strong department to a middling one overnight.</p>
<p>Proof? Philosophy is in important ways a similar field to Classics---a core humanities field with an ancient academic pedigree, but not the most popular undergrad major. There's been relatively little movement since the 1995 NRC rankings of philosophy faculty quality, as measured by an independent 2006-08 survey of philosophers reported by the Philosophical Gourmet. The methodologies of the two surveys are different, but the rankings not so very different---some relative jockeying around, most schools moving up or down only a few slots over that interval, with just a couple of outliers. Here's the 1995 NRC ranking, with the school's 2008 Philosophical Gourmet ranking following in parentheses:</p>
<p>1995 NRC/School/(2008 Philosophical Gourmet):
1 Princeton (3)<br>
2 Pittsburgh (5)<br>
3 Harvard (7)<br>
4 UC Berkeley (12)<br>
5 UCLA (7)<br>
6 Stanford (6)<br>
7 Michigan (4)<br>
8 Cornell (16)<br>
9 MIT (7)<br>
10 Arizona (13)<br>
11 Chicago (20)<br>
12 Rutgers (2)<br>
13 Brown (16)<br>
14 UC San Diego (20)<br>
15 Notre Dame (13)<br>
16 UNC Chapel Hill (10)<br>
17 U Illinois Chicago (35)<br>
18 CUNY (23)<br>
19 U Mass Amherst (24)<br>
20 UC Irvine (20)<br>
21 Wisconsin (24)<br>
22 Syracuse (32)<br>
23 Ohio State (26)<br>
24 Northwestern (53)<br>
25 Texas (13)<br>
26 Penn (27)<br>
27 Columbia (10)<br>
28 Boston University (50)<br>
29 Indiana (27)<br>
30 Johns Hopkins (35)</p>
<p>Notice that not a single school ranked in the top 15 in the 1995 NRC ranking fell below #20 in the 2008 Philosophical Gourmet ranking. To be sure, there was movement within this group: Rutgers leaped from 12 to 2, Berkeley fell from 4 to 12, Cornell from 8 to 16, Chicago from 11 to 20. But these are still extremely strong faculties; it's no demerit to be ranked the 20th-best philosophy faculty in the country, even if you were ranked 11th-best over a decade ago. And most schools that started out at or near the top in the 1995 rankings moved only 3 or 4 spots up or down---essentially just statistical "noise." Farther down the rankings, a couple of schools---Northwestern and Boston U---fell more precipitously, but this may be the result of (what is alleged by its critics to be) methodological bias in the Philosophical Gourmet survey in favor of analytical philosophy and against continental philosophy, in which both Northwestern and BU have been particularly strong. The University of Illinois-Chicago also fell, but this is overall a weaker school that lost some top people and apparently found them more difficult to replace than would a Princeton, Harvard, Michigan, or Stanford, for reasons that are obvious if you think about it.</p>
<p>(more below)</p>