Buried by Putnam himself. From Wikipedia:
"In recent years Professor Putnam has been engaged in a comprehensive study of the relationship between trust within communities and their ethnic diversity. His conclusion based on over 40 cases within the United States is that, other things being equal, more diversity in a community can mean less trust both between and within ethnic groups.
"Putnam has not yet published this work. In 2006, Putnam was quoted in the Financial Times as saying he had delayed publishing this research until he could "develop proposals to compensate for the negative effects of diversity" (quote from John Lloyd of Financial Times)
" In 2007, writing in City Journal, John Leo questioned whether this suppression of publication was ethical behavior for a scholar, noting that "Academics arent supposed to withhold negative data until they can suggest antidotes to their findings."
More like: "develop proposals to compensate for the negative effects on my career and reputation for writing this"