Rival Organizations Bicker Over the Best Way to Evaluate Nonprofit Groups for Donors

Few questions vex the nonprofit world more than how donors should decide which charities to support. A proliferation of charity-ratings services has popped up in recent years, including GreatNonprofits, which asks the public to review charities like they would a consumer product, and GiveWell, which performs in-depth studies on a small number of groups to see how effective they are.

Two groups that have been around for a while—Charity Navigator and CharityWatch—have for