New York City is the safest big city in the nation. The city is betting it can [get even safer]. The Mayor's Action Plan for Neighborhood Safety is being employed in 15 of the most dangerous public housing complexes in the city. The idea is to lower crime by making these neighborhoods better - places where residents live in well-maintained buildings, have necessary services, are engaged in civic life and can collaborate to solve problems. Working elevators, summer jobs for teenagers, community centers open till midnight, residents who know what to do when the trash piles up - no one would doubt that these are good things. But it seems a stretch to call them crime prevention measures. Will people really commit fewer robberies and shootings if the trash gets picked up? Crime has dropped more in the 15 complexes involved in the plan than in other public housing. Why? It might be this: Crime is in part a function of trust. "Trust is the heartbeat of civic life," said Elizabeth Glazer, head of the Mayor's Office of Criminal Justice. "These neighborhoods feel completely estranged." Perhaps more important ... is what social scientists call "collective efficacy" - achieved when neighbors feel that they can trust and rely on one another and work together to get things done. Collective efficacy is so important that the lack of it - common in disadvantaged neighborhoods - is most of the reason poor communities have more crime. When they build collective efficacy, even without other changes, crime drops.