It’s harder for women to become CIOs than it is for them to achieve any other executive role, according to researchers at the University of California, Davis. A recent study by the university’s Graduate School of Management found only four female CIOs at the 200 largest public companies headquartered in California.

Although there are few women in C-level jobs at any of the 200 companies, 32 percent have female executive officers and 66 percent have women as directors.

The percentage of women who are CIOs is similar elsewhere in the United States, says Kim Elsbach, professor of management and coauthor of the study. For example, she says a study by InterOrganization Network counted only two women out of 100 CIOs in Massachusetts.

June Drewry, CIO with the insurance company Chubb, says there’s more to the problem than discrimination – including career decisions women make and how well-known they are to upper management.