The idea that where you end up depends, at least in part, on where you start from has gained currency among those who study crime, poverty, and public health issues. It might be plain commonsense to assume that neighborhoods have an influence on their inhabitants, but research has yet to discover which aspects are most influential and exactly how they affect individuals.

Felton Earls, a professor of behavior and development at Harvard School of Public Health, is among those who are beginning to shed light on the key questions. In the course of Chicago neighborhoods, he found that children growing up in communities rich in a quality he calls 'collective efficacy' – even those who displayed many other 'risk factors', such as poverty or a lone parent, fared better than those living without it elsewhere.

Indeed, Earls and his colleagues found collective efficacy to be so important that they are now testing its impact in a completely different and more difficult context – in Tanzania, part of sub-Saharan Africa, one of the world’s poorest regions.

Earls’s career path, which began in medical school, made a sharp turn following the death of Martin Luther King in 1968. "King's death made me see that I had to work for society. My laboratory had to be the community, and I had to work with children because they represent our best hope,” he told The New York Times in 2004.

For their multi-million dollar study Earls and his colleagues chose as their “laboratory” 196 neighborhoods in Chicago. The project aimed to examine the relationships of crime and violence to characteristic social, familial, educational and personal factors.

To study these connections as precisely as possible, the team collected a wealth of information including police records on homicide, robbery and burglary. They surveyed 8,782 residents. and even toured 11,408 blocks in slow-moving trucks videotaping street-scapes and street-level activities. Researchers found that neighborhoods with greater collective efficacy – defined as “social cohesion among neighbors combined with their willingness to intervene on behalf of the common good” – were less prone to be violent.

Prior to this study, the conventional wisdom was that poverty and race were the primary predictors of violence in neighborhoods. Earls’s work showed on the contrary that there were poor, black neighborhoods with lower rates of violence than white, middle-class neighborhoods. What distinguished them were their varying levels of collective efficacy, which also seemed to reduce other problems such as low birth weight, asthma, and mental health issues. The implications for policy were clear: governments should support local efforts such as community policing and even community gardening that bring residents together to invest in their neighborhoods.

Tanzania, whose government subsequently said it was interested in testing the study findings, is struggling to deal with the HIV/AIDS epidemic, and Earls and his colleagues are in the process of testing a program to strengthen community approaches to promoting the health and well-being of children. The study there includes 30 neighborhoods, some of which have been randomly chosen to foster collective efficacy, and some of which will be used as points of comparison.

Like its Chicago predecessor, the Tanzania project involves thoroughly mapping community characteristics, particularly the health of community members. Although the Earls team lay out the basics of the program, they are collaborating with 10-14-year-old children (called “youth citizens”), who are being educated in health issues and encouraged to organize activities that address the health of the community, particularly through dramatic presentations. The hope is that empowering children in this way will help to breed a sense of collective efficacy, which will spread throughout the communities and, in turn, reduce the spread of HIV/AIDS.

The project began in 2003 and is scheduled to end this year with study results to follow.