PRAGUE — When disaster strikes, nongovernmental organizations are among the first on the scene. The United Nations estimates that there are now more than 37,000 international NGOs, with major donors relying on them more and more.

Inevitably, there are problems. Both the Rwandan genocide of 1994 and the 2004 Indian Ocean tsunami saw chaotic competition among NGOs. Yet there have also been landmark successes.

More than 1,400 NGOs operating in 90 countries helped to get 123 countries to ratify the treaty banning land mines. But the sheer scale of the disaster relief "industry"— plus the longer-term development efforts of NGOs — is raising serious concerns about how to measure their performance.