“Nonprofits were more likely to form in the communities with the gravest problems. But they also sprang up for reasons that had little to do with local crime trends, such as an expansion in philanthropic funding. A spike in nonprofits addressing subjects like the arts and medical research occurred in this same era. Comparing the growth of other kinds of nonprofits, the researchers believe they were able to identify the causal effect of these community groups: Every 10 additional organizations in a city with 100,000 residents, they estimate, led to a 9 percent drop in the murder rate and a 6 percent drop in violent crime.”