Data collection for the most recent report began in June 2006; it was released on September 28, 2010. These rankings did not provide exact ranks for any university or
doctoral program; rather, a statistical range was given. This was because "the committee felt strongly that assigning to each program a single number and ranking them accordingly would be misleading, since there are significant uncertainties and variability in any ranking process." Two series of rankings were offered: • The
R-rankings were based on
regression analysis. According to the NRC, this analysis was "based on an indirect approach to determining what faculty value in a program" and was done by first asking a sample faculty group to rate a number of programs in their area, and then using a statistical analysis "to calculate how the 20 program characteristics would need to be weighted in order to reproduce most closely the sample ratings." In doing so, the rankings "attempted to understand how much importance faculty implicitly attached to various program characteristics when they rated the sample of programs." Weights were assigned to each of characteristic varied by field. The factors included in these computations included the number of publications per faculty member,
citations per publication (except in computer science and the
humanities), fraction of the faculty supported by grants and number of grants per faculty member, diversity of the faculty and students, student
GRE scores, graduate student funding, number of Ph.D.s and completion percentage, time to degree, academic plans of graduating students, student work space, student health insurance, and student activities. ==Reception==