Although women get most kinds of cancer just about as much as men do, they're still not participating in clinical studies as often, reports a new study published online today in the journal Cancer.

The study analyzed participants in 661 papers published in eight "high impact journals" (including Cancer, Journal of the American Medical Association and New England Journal of Medicine) and found that women made up an average of 38 percent of non–sex specific cancer study participants. For example, although women contract just a bit less than 50 percent of gastrointestinal cancers, they made up less than 40 percent of the trials for those cancers.

"It's so important that women are appropriately represented in research," lead study author and assistant professor of radiation oncology at the University of Michigan Medical School, Reshma Jagsi said in a statement. "We know there are biological differences between the sexes, a well as social and cultural differences. Studies need to be able to assess whether there are differences in responses to treatment."

Government-funded studies, which are under a 1993 directive from the National Institutes of Health (NIH) to enroll both more women and minorities, had a slightly higher share of female participants at 41 percent.

So why aren’t there more women in studies? It may be more difficult to recruit them: Jagsi noted that women are already having to balance "domestic responsibilities, their cancer diagnosis, and often a career as well." She recommends offering more money to cover extra childcare or transportation expenses.

A 2007 study published in the same journal outlined the difficulties in recruiting other underrepresented groups—including racial minorities, those with lower income, rural residents and older adults—to participate in cancer trials. Whites, for example, still made up more than 88 percent of those enrolled in publicly funded cancer clinical trials between 2003 and 2005, according to the Intercultural Cancer Council at the Baylor College of Medicine in Houston. That’s despite the fact that U.S. blacks still die more frequently from cancer than whites.

Image courtesy of iStockphoto/LilliDay