It could mean stepping in to keep a drunk woman from being whisked away from a party, calling over a bouncer or creating a noisy distraction at a bar, or just letting someone know that a rape joke isn't funny.

So-called bystander intervention tactics are emerging as a preferred strategy as colleges across the country look for ways to strengthen sexual assault prevention efforts.

It may seem like common sense to intervene — do something, say something — when a dangerous or potentially harmful situation presents itself. But stepping in, even subtly, can be tricky, particularly in unfamiliar situations, such as those arising at parties during freshman year.

Police say such involvement was lacking in two incidents in dormitories at Ramapo College in Mahwah, N.J., and William Paterson University in Wayne, N.J., last month that led to sexual assault charges.

In both cases, two men were charged with sexually assaulting a female student while three bystanders were accused by police of aiding and abetting the attack.

"It's fair to say that people watched the event occur and didn't intercede," Mahwah Police Chief James Batelli said of the Ramapo attack, in which another female student was among those charged with invasion of privacy and failure to render aid.

Ramapo President Peter Mercer said the lack of intervention was "distressing" amid the college's emphasis on teaching bystanders to step forward.

He has promised a full review of the school's policies and procedures on sexual violence, as has William Paterson University President Kathleen Waldron.

Similar efforts are taking place nationwide as schools, pushed by the federal government, attempt to strengthen sexual assault prevention and response.

The efforts are many — seminars, social media campaigns, pledges, surveys, new legal requirements and more — and largely unproven. They seek to change a culture in which it is estimated that as many as one in five students is sexually assaulted. Although the one in five figure has become a rallying cry for those seeking change, critics have complained that the definition of sexual assault in the survey that led to that figure is too broad and the sample size too small to be reliable.

Regardless of the scope of the problem, some experts believe that bystander intervention is the most effective strategy for stanching it.

"If you look at bystander intervention, the beauty of it is it puts the responsibility in the community," said Ruth Ann Koenick, director of the Office for Violence Prevention and Victim Assistance at Rutgers University.

The concept requires a fundamental shift, however, one that recent assaults may show still has a way to go.

Many programs, like the one at Rutgers, have employed role playing and interactive skits to help students practice how they would react in different situations.

Experts stress that intervention can take many forms, and caution students to respond in ways that feel safe and appropriate.