Ønsker dere full stopp av innvandring fra ikke-vestlige land, eller har dere en genial måte å skille voldtektsmenn og andre kriminelle fra de som er her for å skape seg et bedre liv?

In recent years, 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 and 30 000 people within the United States is that, other things being equal, more diversity in a community is associated with less trust both between and within ethnic groups.

Although limited to American data, it puts into question both the contact hypothesis and conflict theory in inter-ethnic relations. According to conflict theory, distrust between the ethnic groups will rise with diversity, but not within a group. In contrast, contact theory proposes that distrust will decline as members of different ethnic groups get to know and interact with each other. Putnam describes people of all races, sex, socioeconomic statuses, and ages as "hunkering down," avoiding engagement with their local community—both among different ethnic groups and within their own ethnic group. Even when controlling for income inequality and crime rates, two factors which conflict theory states should be the prime causal factors in declining inter-ethnic group trust, more diversity is still associated with less communal trust.

• Lowered trust in areas with high diversity is also associated with:
• Lower confidence in local government, local leaders and the local news media.
• Lower political efficacy – that is, confidence in one's own influence.
• Lower frequency of registering to vote, but more interest and knowledge about politics and more participation in protest marches and social reform groups.
• Higher political advocacy, but lower expectations that it will bring about a desirable result.
• Less expectation that others will cooperate to solve dilemmas of collective action (e.g., voluntary conservation to ease a water or energy shortage).
• Less likelihood of working on a community project.
• Less likelihood of giving to charity or volunteering.
• Fewer close friends and confidants.
• Less happiness and lower perceived quality of life.
• More time spent watching television and more agreement that "television is my most important form of entertainment".

Putnam published his data set from this study in 2001 and subsequently published the full paper in 2007.

Putnam has been criticized for the lag between his initial study and his publication of his article. In 2006, Putnam was quoted in the Financial Times as saying he had delayed publishing the article 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 aren’t supposed to withhold negative data until they can suggest antidotes to their findings."