Yale may be stepping up efforts to recruit students from middle-income families, but the University has come under fire in the past week for enrolling what several higher-education observers say is an insufficient number of students from the lowest income brackets.

The percentage of Yale students receiving federal Pell grants — which are generally given to those in the lowest income quartile — has decreased by 14 percent over the past eight years at the same time that Yale’s multi-billion dollar endowment has grown exponentially, according to a study by Pell Institute senior scholar Tom Mortenson. But Dean of Admissions Jeff Brenzel said he disputes Mortenson’s conclusions, arguing that the percentages of both Pell students and students from slightly wealthier families have crept upward in the past few years and will continue to do so.

Brenzel said the percentage of students receiving Pell grants has increased in the last four years, but he prefers to focus on the percentage of enrolled students from families making under $60,000 a year as a marker of Yale’s success in attracting low-income students.

The percentage of students receiving Pell grants rose from 9.1 percent in the class of 2008 to 10.8 percent in the class of 2011, Brenzel said. The percentages of Pell students in the classes of 2009 and 2010 are 9.8 and 9.4 percent, respectively, he said.

But the increase in the number of Pell grant students over the past four classes reported by Yale is not statistically significant, statistics professor Lisha Chen said.

“The problem is that we only have four data points,” Chen wrote in an e-mail. “In general we hardly can say anything about statistical significance on a data set this small.”

The admissions office expects these numbers to continue to increase over the next few years, Brenzel said, due to recruitment efforts and aid initiatives.

“We are watching these numbers and striving to move them forward, and I was glad to see the number in fact move forward this past year,” Brenzel said in an e-mail. “The significance of year-to-year moves should become clear over time.”

Pell grant recipients generally come from families making below $40,000 annually, which is just under the nationwide median household income of $48,000.

Mortenson said he was especially concerned about the 14-percent drop in Pell students at Yale in the past eight years, given that the percentage of Pell students at Harvard University increased by 53 percent over the same time period, according to his Dec. 2007 analysis.

As the percentage of low-income children in the K-12 school system increases, Mortenson said, Yale has a responsibility to help educate these students — a responsibility that it is not meeting.

“The real question is, ‘Who is trying to deal with this huge demographic tide, and who isn’t?’” Mortenson said. “As I look at Harvard’s data, I say Harvard is, and as I look at Yale’s data, I say Yale isn’t.”

Yale’s recent announcement of an unprecedented increase in undergraduate financial aid did not change his analysis.

Mortenson called Yale’s new financial-aid initiative — which dramatically reduces the expected parental contribution from families making up to $200,000 a year and eliminates the need for student loans — a mere “public-relations gesture.”

He suggested that Yale, which along with other wealthy universities is facing scrutiny from Congress over the money it spends from its endowment each year, had gone forward with the aid initiative — and, in the process, increased endowment spending — in order to forestall congressional intervention.

But Student Financial Services Director Caesar Storlazzi defended the University’s efforts to recruit low- and middle-income families.

One of the obstacles to admitting more low-income students is that the admissions process is, by design, need-blind, Storlazzi said. As a result, while admissions officers do not discriminate against needy students, they also cannot use numerical needs analyses to give them an admissions boost, he said.

“Admissions officers cannot be expected first to do a needs analysis and then admit them,” Storlazzi said. “This runs completely counter to the philosophy of need-blind admissions. The best they can do is look at the students’ family employment and their location and make certain assumptions about income levels, but even those can be incorrect.”

In addition, Yale and Harvard are vying for a fairly small pool of qualified Pell recipients, he said.

As a result, if Harvard reports having a higher percentage of those students, it does not necessarily indicate that Harvard is more generous or sensitive to low-income students, Storlazzi said. Rather, it reflects the fact that students often choose Harvard over Yale when given the choice because of Harvard’s brand-name recognition, he said.

Yale’s endowment grew by 28 percent in the fiscal year that ended June 30, reaching $22.5 billion. Harvard’s, meanwhile, increased by 23 percent, to $34.9 billion.

The Senate Finance Committee announced last week that it would request detailed information concerning aid, tuition and endowment spending from more than 100 of America’s wealthiest universities.

Other studies have also found Yale lagging behind Harvard in its numbers of Pell grant students. The Journal of Blacks in Higher Education published a study in the fall showing that only 9.4 percent of Yale College students receive Pell grants, compared to 12 percent of Harvard undergraduates.

Of the 10 wealthiest American universities, the study reported, only Harvard had increased the percentage of Pell grant recipients from 2004 to 2006, from 9.4 percent to 11.9 percent.

But the Journal’s managing editor, Bruce Slater, declined to call Harvard’s increase progress.

“The gains at Harvard are not all that spectacular to begin with,” Slater said. “Although Harvard has gone up and Yale has not, I don’t think that’s significant.”

The Harvard financial-aid office did not respond to a request for comment.

Slater said that while Yale’s new aid plan will help the low-income students who do end up at Yale, the University needs to do more to encourage these students to apply in the first place.

Brenzel explained how the use of Pell grant data may be unreliable when forming statistical conclusions. The application procedures and requirements for Pell grants shift periodically, he said, making those data somewhat unstable over time. Foreign students are also not eligible for Pell grants, he pointed out.

Instead, he said, the office looks at students under the $60,000 mark, which is slightly under the $65,000 median income for families with college-age students.

Yale announced in the fall that 15.1 percent of the class of 2011 came from families making below $60,000, up from 13.7 percent in the class of 2010. At the time, three statistics professors interviewed by the News called this change statistically insignificant.

Yale announced in mid-January that it will require no parental contribution from families making less than $60,000 annually. Families making between $60,000 and $120,000 will pay up to 10 percent, on average, of their income toward tuition, while families making between $120,000 and $200,000 will pay an average of 10 percent of income.