There is no statistical measure of how successful the Yakima Police Department’s block watch program is at preventing crime. But based on national studies of similar programs, it’s probably helping at least a little — even if the benefits aren’t tangible.

The department doesn’t keep track of which crime-reporting calls come from participants in the program, which includes about 100 block watch groups. But Nikki Sandino, who along with Amy Hayes administers the program through the department’s Community Services division, said there have been times when block watch participants have alerted the police and neighbors to crime or suspicious activity that otherwise may have gone unreported until much later.

“The first step is always calling 911 and reporting it,” Sandino said. “The second step is reporting it to your neighbors.”

That’s essentially the model in place since the National Sheriffs Association formally launched its national neighborhood watch program in 1972. There are now more than 30,000 groups nationwide, and they have varying levels of active patrolling, said John Thompson, deputy executive director of the National Sheriffs Association. Some meet up and walk their neighborhoods, doing things like writing down license numbers of unfamiliar cars. Others, such as those in Yakima’s program, pledge to report suspicious activity but don’t actively patrol for it.

In either case, their presence can have a chilling effect on neighborhood crime, he said. Block watch groups in Yakima, like other places, mark their territory with signs warning away potential criminals.

“You can’t find any better crime-fighting tool,” Thompson said. “You think a guy who’s going to break into a house is going to break into one where there’s a neighborhood watch or one where there isn’t?”

There’s also the matter of what criminologists refer to as “collective efficacy” — neighbors looking out for one another.

“Research shows that neighborhoods with high collective efficacy experience greater public safety and reduced crime even when controlling for factors like poverty,” said Edmund McGarrell, a Michigan State University criminal justice professor who since 2002 has researched crime prevention as a partner in the Department of Justice’s Project Safe Neighborhoods program. “Thus, a sound crime prevention strategy is to build collective efficacy — connections between neighbors and a collective sense of looking out for one another. Block Watch can be a way of doing this.”

Still, studies of neighborhood watch effectiveness have shown mixed results. The most widely cited study, “Does Neighborhood Watch Reduce Crime?” a meta-analysis commissioned by the Department of Justice and published in 2008, combined 18 previous studies before reaching the conclusion that “some programs work well while others appear to work less well or not at all.”

Overall, that meta-analysis indicated a 16 percent decrease in crime in areas with neighborhood watch. But it emphasized the lack of hard data supporting that number. It also found that the areas that could most benefit from neighborhood watch are the least likely to participate.

“Areas where they could do the most good are areas that lack the collective efficacy,” said David Makin, a Washington State University criminal justice professor who has taught graduate courses on policing and society.

That could be because people in poorer neighborhoods mistrust the police based on previous negative interactions or because they’re struggling to get by and don’t have time to participate, he said.

“It’s much more difficult to do when you’re working multiple jobs,” Makin said.

There’s also the matter of potential negative consequences of neighborhood watch. The 2012 shooting death of 17-year-old Trayvon Martin, who was killed by neighborhood watch member George Zimmerman in Florida, is a famous example. But it’s more likely to be a run-of-the-mill harassment by overzealous citizens, he said.

“The saying is ‘See something, say something,’” Makin said. “And that’s OK. But how do you know who doesn’t belong in your neighborhood? Your fallback is stereotypes.”

That’s why every Yakima block watch begins with a block-party organizing meeting at which police representatives meet with neighbors to discuss what should be reported: Things like strangers trying to open doors, youths in the neighborhood during school hours, people peering into parked cars or people carrying household property on foot. In addition to education, those organizing meetings also go a long way toward fostering collective efficacy, Sandino said.

“We’ve gone and done block parties where someone has lived with a neighbor on the same street for 10 to 15 years and never met them before that day,” she said. “When you know somebody, you’re more invested in helping them and helping them protect their belongings.”

Sandino also emphasized that the Yakima Police Department discourages overzealous block watchers.

“It’s not about going on nightly patrols,” she said. “And it’s not about confronting people in your neighborhood. It’s about just being observant.”

Thompson of the National Sheriffs Association concurred.

“Anybody who joins it thinking they’re going to be law enforcement or a vigilante or going to go out and engage people, that’s not what it’s about,” he said.