His extensive research found that the more diverse a community, the less likely were its inhabitants to trust anyone, from their next-door neighbour to their local government. People were even more wary of members of their own ethnic groups, as well as people from different backgrounds.
Now this in itself is hardly suprising. It is intuitively plausible, since the less you know or can infer about someone, and the less you are able to deliver social sanctions through social networks, the less rational it is to trust them. Andrew Leigh (who has worked with Putnam in the past) has already written a good study of it, reporting some international empirical work and adding Australian evidence. This story should just have been telling us that we were about to get some interesting extra detail. But instead it suggests that Putnam himself should be treated with some intellectual distrust.
The original Financial Times report said:
Professor Putnam told the Financial Times he had delayed publishing his research until he could develop proposals to compensate for the negative effects of diversity, saying it