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If you've ever taken a psychology class, you've probably heard the shocking story of Kitty Genovese. As the story goes, she was murdered one night in 1964 with 38 witnesses, yet no one helped or even called the police until it was too late.

Reports about this horrible, bizarre event sparked research on what came to be known as the bystander effect. Despite what you'd think, it says that, sometimes, someone is actually less likely to help if there are others around. But even though it's talked about in every intro psych course, the bystander effect isn't as simple as “more people equals worse odds of getting help.” Sometimes, more is better, and there are other factors that matter, too.

Oh, and also? That original story of Kitty's murder isn't entirely true. After the New York Times published their story about Kitty Genovese, scientists set to work trying to figure out why so many witnesses hadn't responded.

The first major study was published in the Journal of Personality and Social Psychology in 1968. In it, two researchers created a similar situation in the lab. They had 72 undergrads come in to what they thought was a study on common problems in students' lives.

Each participant was seated alone in a room with an intercom to share their problems with one, two, or five other so-called “participants" — although they were actually recordings. Then, one of these pre-recorded participants pretended to have a seizure, and the scientists timed how long it took for the undergrad to get help. They found that the more bystanders there were, the longer it took — if they got help at all.

When they were alone, 85% of participants got assistance. But in the largest group of five bystanders, only 31% did. Admittedly, most people were concerned about the sick person, but they didn't know if they should do something.

And so the bystander effect was born. Since then, multiple studies have confirmed this effect, but they've also found it isn't always as straightforward as it seems. Sometimes, people are more likely to help with bystanders, or simply aren't affected by their presence.

One major influence on this is the bystanders themselves. Not surprisingly, people who are in a hurry are typically less likely to stop and help someone. And people who are highly skilled in a certain emergency — like nurses trained to handle medical situations — are also more likely to try to help, whether bystanders are there or not.

More interestingly, though, making a commitment also matters. In a 2015 study in France, a man sat down his bag and asked either one specific person to watch it, everyone in general to watch it, or said nothing, then headed to a nearby. ATM.

Then, the researchers faked the backpack getting stolen. They repeated trials of this until they had a total of 150 different bystanders — 50 for each scenario. Ultimately, the more direct of a commitment, the more likely people were to intervene when someone took the bag.

Other studies suggest that responses in situations like this have to do with a couple of things. One is social influence. In general, when you aren't sure what is going on, you probably tend to look at other people for more information.

And if no one else seems to be concerned, then maybe this guy's backpack isn't a big deal — so you don't do anything, just like everyone else. Another factor is diffusion of responsibility. If something happens when you're in a big group — like some participants in this backpack study — it isn't up to only you to help.

Other people could help too. So, you don't feel as responsible and don't act, and suddenly that man's out of a bag. Besides the bystanders, another major factor in general is the specific situation.

Sometimes, it's hard to tell if someone needs help or not. And many studies have found that when things are ambiguous, people are less likely to jump in. Which seems reasonable.

After all, if it turns out someone is just playing around, it could be really embarrassing to be wrong. Research suggests that ambiguous situations can make people fear being judged negatively, which can stop them from acting. The good news is that when it's clear that there is an emergency, the bystander effect doesn't usually happen.

A 2011 meta-analysis of more than 50 studies also showed that if the situation is dangerous, like if the perpetrator is still there, people are more likely to help if there are bystanders. And that makes sense. Those situations are clearly an emergency, and it's safer if other people have your back.

Ultimately, although there are some trends, a lot of different social and psychological factors determine whether or not someone will offer help. Today, research suggests that your best bet in an emergency is to make it clear that you do need assistance, and to make individuals feel responsible for stepping in. Really, though, it isn't that surprising that this effect isn't totally straightforward.

Humans aren't exactly clear-cut, so the bystander effect isn't, either. Even the original Kitty Genovese story wasn't as black-and-white as the New York Times reported. * The truth is, 38 people did not witness the murder. When Kitty was first attacked on the street, many may have briefly heard something, but only a handful of people saw anything happening in the dark.

And even then, it was the middle of the night, and it was hard to tell what was going on. In other words, it was ambiguous. One person scared the attacker away by yelling out the window, and, injured, Kitty tried to get to her apartment.

Then, unfortunately, in the building's entrance where people couldn't see or hear her very well, the attacker came back. Police were called but didn't arrive until it was too late to save her. The newspaper article wasn't published until two weeks after the event, so there was time for details to get a little fuzzy.

Thankfully, we have researchers studying this phenomenon to make sure that's less likely to happen again. Thanks for watching this episode of SciShow Psych! If you'd like to dig deeper into some of the topics you might've covered in Psych 101, you can watch our episode about Maslow's Hierarchy of Needs.

Turns out, that's not as helpful as you'd think, either. [♪ OUTRO ].