A new study reveals that the answer to that key question varies dramatically depending on who you ask—or, to be more specific, by the age and gender of who you ask.

The survey includes more than 4,000 corporate board directors in 60 countries, though U.S. board members accounted for almost half of respondents. It was conducted by several researchers—including two from Harvard Business School, in partnership with the WomenCorporateDirectors Foundation and executive recruiting firm Spencer Stuart.

While the researchers touch on a number of questions, there’s one that stands out: “What is the primary reason that the number of women on boards is not increasing?”

Among male directors, the overwhelming response is “lack of qualified female candidates.” Older men were the most likely (42%) to pin the problem on the candidate pool, but it was also the No. 1 response of male directors age 56 to 65, and the second-most popular response (24%) of men 55 and younger.

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Perhaps not surprisingly, women have a different perspective. Female respondents largely dismissed the idea that there no prepared women candidates. Instead, they zeroed in two factors: male domination of traditional networks, which boards tend to tap when looking for new members (43% of women over 65 cited this as a problem) and boards failure to make diversity a factor in recruiting (69% of women 56 to 60 choose this response).

Perhaps this difference of opinion is related to another finding from the study: Female directors are more like to favor term limits (68% of women vs. 56% of men) and mandatory retirement ages (57% of women vs. 39% of men) than their male their male counterparts.

It’s easy to understand their thinking: After all, if current board members won’t open their minds to different types of candidates, perhaps it’s time for new board members?