Harvard may be used to bucking national trends, but in math and computer science, its relationship to the national gender gap is more complicated.

Nationally, the number of incoming female undergraduates choosing computer science as a major declined 70 percent between 2000 and 2005, according to the National Center for Women & Information Technology. The trend is part of a quarter-century decline in female computer-science majors detailed in a New York Times article on Saturday.

At Harvard, the story looks different, but not necessarily any better.

Over the past year, female enrollment in Computer Science 50 has jumped 60 percent. But A. Cansu Aydede ’11, a female computer-science concentrator and a teaching fellow for CS50, says she suspects the jump in enrollment is due primarily to the accessible and welcoming approach of the professor, David J. Malan ’99. And it remains to be seen whether an increase in the number of students taking the introductory class will translate to a higher number of concentrators.

Women currently make up a slightly higher share of Harvard computer-science concentrators than they did each of the last six years. But this is largely because the overall number of concentrators has dropped by 30 percent. As of last year, Harvard had just four female computer-science concentrators out of a total of 23.

“Our concentrators have been decreasing since the end of the Internet boom,” said Ellen Holloway, the School of Engineering and Applied Sciences academic programs administrator. “There were twice as many five years ago, but also twice as many concentrators,”

The gender balance is more skewed in computer science than in other normally male-dominated fields, such as applied mathematics and engineering. While applied mathematics and engineering have seen five and three percent declines in female concentrators since 2002, both fields still have a larger percentage of female concentrators than computer science.

In the 2007-2008 academic year, women numbered 38 percent of engineering concentrators and only 17 percent of computer-science concentrators.

According to Joanne Cohoon, a research scientist at the National Center for Women & Information Technology, this trend is nothing new. Female enrollment in computer-science courses has been declining since the 1980s. The push to establish computer science as an independent discipline with specialized knowledge “hardened” the image of computer scientists “into something stereotyped as masculine,” she said.

In addition, as the number of students in the field increased, the size of the faculty could not keep up, leading some schools to set caps on the number of students who could enter the field.

“That process of setting up barriers for entry combined with the more prevalent stereotype of this being a masculine activity meant it was harder to get into, and women were now getting the message that they didn’t really belong there,” Cohoon said.

Malan said he believes that this psychological factor still affects the number of females who choose computer science. In terms of academic performance, “we see no difference between male and female students,” he said.

Aydede said she believes that stereotypes discourage females from studying computer science starting in high school.

“In high school I was intimidated by computer science,” she said. “It was just a bunch of guys.”

Nationally, Cohoon said her center is making an effort to highlight aspects of occupations in computer science that are attractive to women, such as the flexibility to work in a number of different fields and locations, as well as the creative aspect of the job—a trait that she called characteristically feminine.

While there has been no organized effort to attract more female students into computer science at Harvard, Malan said he openly acknowledged the gender imbalance in his course on the first day of the semester, and encouraged female students to enroll anyway.

“I hope the problem begins to chip away at itself,” he said. “As numbers begin to equalize, the perspective will change.”