Looks like proactive Ombuds work to me:

When National Public Radio Ombudsman Alicia Shepard wrote about gender imbalance among NPR's sources and commentators last week, she made a bold claim: "The network is not as diverse on air as it would like to think."

Shepard, with the help of two NPR interns, spent a little over a year collecting data on the network's commentators, reporters and hosts, and on the sources interviewed for stories.

..."I wish I could say I was surprised," Shepard told me by phone when I asked her about the imbalance. "I've gotten one or two complaints from listeners about this, but this [study] was not driven by listeners. This was driven by me as a listener and by my familiarity with NPR."

...Some people at NPR took issue with the way Shepard collected the data for her study. "Morning Edition" host Steve Inskeep pointed out that the data counts all sources as the same, without factoring in the length of time each source was on the air.

Read the full article [here].