GW continued its more than decade-long dance around the top 50 schools in the country, dropping to No. 51 in the U.S. News and World Report rankings Tuesday.

The slight slump reflects a tepid showing in categories like six-year graduation rate, acceptance rate and standardized test scores, holding GW back, despite improvements in freshman retention and faculty salaries.

GW accepted 33 percent of students in last fall’s freshman class, making it less selective than the year before, when it accepted about 31.7 percent. Acceptance rate factors into a larger category that accounts for 15 percent of universities’ scores.

Standardized test scores also stagnated last year, with average SAT scores coming in again at 1300.

Graduation and retention rates make up one-fifth of the entire ranking. U.S. News factors in student selectivity for the fall 2011 class for 15 percent of the ranking. Indicators like financial resources, alumni giving, graduation rate performance each make up 10 percent or less of the ranking.

GW tied at No. 51 with Boston and Tulane universities this year, after cracking into the top 50 last year for the first time since 1998.

Though few schools usually catapult in the rankings from year-to-year, Rensselaer Polytechnic Institute, which tied at No. 50 with GW last year, jumped to No. 41 this year. GW’s peer schools, like University of South California and Tulane, were both named among U.S. News’ “up-and-coming schools,” ranked No. 24 and No. 51 overall, respectively.

Robert Morse, director of data research of U.S. News, said the ranking methodology is set up to give stronger weight to what a school is able to achieve – like graduating and keeping more students.

Those measures may have dragged GW down even though it has boasted rising numbers in categories like the high school achievement of its incoming freshman class. More than three-fourths of last year’s freshman class were in the 10 percent of their high school classes – an 11-percent jump from 2008 and 2009.

“You have to look at the factors that U.S. News uses, and you have to make across-the-board, incremental improvement. It can’t be just one factor,” Morse said. “It has to be across-the-board, step by step, like walking up a ladder. Each year you do something.”

Subjective measures like undergraduate academic reputation and high school counselor ratings also make up nearly a quarter of the ranking’s weight.

“We believe that some things can’t be measured just by quantitative data,” Morse said. “Reputation or image of the school matters when a student tries to get their first job or when they apply to graduate school, and this is a way of measuring that and measuring some of the intangibles.”