The fastest-growing part of the U.S. economy is not business, at least not the commercial kind. It’s the nonprofit sector. In the past decade, the number of nonprofit groups has grown by 25 percent to 1.6 million. They now account for 5.4 percent of gross domestic product and 10 percent of jobs.

As the sector has boomed, however, government resources devoted to overseeing it have either declined or stayed the same. That has left considerable room for questionable practices. In recent reports, Bloomberg Markets has explored nonprofits’ use of dishonest solicitations by professional fundraisers whose efforts primarily benefit themselves, the issue of high executive compensation, and the matter of whether groups even deserve to be tax exempt.