

In 1981, a British forensic medical examiner — then called a "police surgeon" — wrote an article for his association's medical journal reviewing 18 examinations he'd done on women who'd claimed to be victims of rape.

His conclusion: 16 of those women must have been lying. In at least one case, his reasoning was as follows: "It was totally impossible to have removed (the victim's) extremely tight undergarments from her extremely large body against her will."

It gets worse: that report actually plays a large role in the current debate over false rape allegations. People often throw around the statistic that studies have shown anywhere from 1.5 percent to 90 percent of rape claims are false; the medical examiner's 1981 study, tight undergarments and all, is the basis for the 90 percent end of that range.

In the past decade or so, academics have started going through the studies on false rape allegations to divide the good research from the bad research. And what they've found is critical for understanding America's ongoing debate about what counts as rape and how it can be proved.

For one thing, research has finally nailed down a consistent range for how many reports of rape are false: somewhere between 2 and 8 percent, which is a lot narrower than the 1.5 percent to 90 percent range of the past. But it's also shown that the cultural debate over rape shapes the reality of how rapes are reported and investigated. The incidents that many people think of as "gray rape" — cases where the victim knew or even dated the offender, where the victim was intoxicated, where the victim didn't fight — are the ones most likely to be treated as false by investigators. But in reality, the rape reports that turn out to be false are more likely to involve strangers and violence.

Who decides whether a rape allegation is false?

At least until the past decade or so, many studies simply reported what police themselves counted as false when hearing and investigating cases. Unfortunately, they couldn't rely on official police records to do it — police don't record whether a crime report is "false." (There is an official police category called "unfounded cases," and it's often used as a proxy for false rape allegations, but they are not the same thing.)

But police assessments of rape allegations often say less about the allegations themselves than they say about the police officers doing the counting. One Scottish study from 1983 quoted a police officer saying, "You get a feel for something and how genuine it is or isn't by the demeanor of the victim ... (and) whether she knows or doesn't know the offender." And studies that rely on the assessment of medical professionals weren't necessarily any better, as the 1981 study about the "tight undergarments" shows.

Until recently, there hasn't been as much research on false rape allegations in America as in other English-speaking countries. And the studies that did exist had the same issues as their British counterparts. One influential study from the 1990s found that in a Midwestern police department, 41 percent of rape claims were found to be false. But the department asked anyone claiming to have been raped to take a polygraph test to prove it — which is strongly discouraged when dealing with potential trauma victims. (The department's policy was to categorize a rape as false only if the accuser recanted, but the threat of the polygraph test could have induced victims to back out.)

The more common an officer thinks false rape claims are, the more likely he is to be skeptical of each new allegation; the more likely he is to conclude that the allegation is false; the higher the numbers of false allegations will be.

Police have historically thought that false rape allegations are much more common than they actually are. (One study of the Philadelphia Police Department from the 1960s found that officers thought that 75 to 90 percent of rape claims were false; the actual proportion found in the study was, at most, 21 percent.) So it makes sense that they're going to be skeptical of each individual allegation. But this is self-perpetuating: the more common an officer thinks false rape claims are, the more likely he is to be skeptical of each new allegation; the more likely he is to conclude that the allegation is false; the higher the numbers of false allegations will be.

This is the key thing to understand about sexual assault statistics: the attitudes that police officers and prosecutors have about when someone's likely to be telling the truth shape the outcomes. For instance, if a police officer assumes a "gray rape" situation — in which the victim didn't explicitly consent to sex but didn't reject it either, or consented while intoxicated — is necessarily just a "he said/she said," then he might not launch a real investigation and find there's more evidence out there.

A 2012 study of the Los Angeles Police Department and sheriff's department, by researchers from Arizona State University and California State University, found a split among law enforcement officers working sexual assault cases. Some of them took an "innocent until guilty" approach to the victim, and others took a "guilty until proven innocent" approach. The researchers found that law enforcement officials who were in the "guilty until proven innocent" camp were more likely to dismiss "he said/she said" cases as unknowable and probably consensual.

In the "innocent until proven guilty" camp, though, detectives emphasized that interviewing the victim was just the start of an ongoing investigation. "Most of the time," one detective told the researchers, "there is something else that can be done" other than talking to victims and suspects: looking at phone records and text messages, evidence from social networking websites, and interviews with potential witnesses. "If I don't go looking for evidence," another said, "I'll never find it." Janine Zweig of the Urban Institute quotes a prosecutor who put it to her more bluntly: "There's always corroborating evidence. You just need to find it."

A growing consensus: between 2 and 8 percent of allegations

There are two ways academics have found to look at rape allegations without all of the cultural baggage that shapes police attitudes. One of them is to conduct independent reviews of case files, to check whether police had a reason to believe a rape claim was false or if their biases were leading them to make assumptions without evidence. The other is to train police officers about the definition of a "false allegation," and then have them start keeping track of the cases they get. Thanks to studies using these tactics, scholars are finally beginning to build a body of research that's methodologically sound and (due to standardized definitions) can be easily compared across studies.

The studies that use one of those two methods have come up with a strikingly narrow range of false accusations: 2 to 8 percent. But the problem is that many of those studies are more than 10 years old, are conducted outside the US, or both.

Many in the media, including Vox, have used a 2010 study of students at one Northeastern university, which found that 5.9 percent of allegations were false, as representative of false rape allegations as a whole — even though the study is inescapably narrow: one university, and only 109 cases. It's used so widely because that study is among the few recent American studies where the case files were being evaluated by the study's authors. But its finding is similar to the other studies that have either looked at case files or come after police training — over several decades, and both in the US and abroad.

On the low end of that range, a 1979 study of rape cases in Philadelphia checked not only police records of rape allegations, but also interviews that each accuser had done with a social worker. In only 3 percent of cases did the social workers find that "investigation shows no crime occurred nor was committed." On the high end, a 1977 study of case files from Toronto found that 10.3 percent of rape cases were based on false reports (though many of the false reports were given by a third party, rather than from the victim). Most other studies — including a more recent study of Australian police reports, and three different studies of British rape reporting over the last 20 years — fall somewhere in between the two.

In fact, the largest study available indicates that it might be at the low end of that range — at least in Great Britain. A 2005 study sponsored by the British Home Office looked at 2,643 rape cases that were reported to police, across six different sites, from 2000 to 2002. Police had classified 8.2 percent of those cases as false reports. But the researchers looked at case files, medical records, and interviews with police victims and service providers. And they found cases where police had classified a claim as false because the victim had mental health issues; had been under the influence of alcohol or drugs; or simply because there were inconsistencies in the victim's statement (which isn't uncommon with victims of trauma). None of these situations were supposed to be classified as false claims under the police's own policy.

When the researchers removed those cases, they came up with a false reporting rate of 2.5 percent — only 67 out of the 2,643 cases that had been reported to police over that time.

"The statistics are actually now in a very small corner of the map"

The largest study that trained police in proper categorization, employing eight American police departments, was conducted as part of the Making a Difference study. (The study data was collected in 2008, but the final report hasn't been published yet.) That study relied on police reports of false claim — but only after police got training and assistance in what counted as a false claim, a baseless claim, or just a claim that needed to be investigated further to see if an arrest should be made. Like the 2010 college study, the Making a Difference study found that about 6.8 percent of rape reports were false.

"At this point," wrote Kimberly Lonsway (one of the authors of the Making a Difference study) in 2010, "there is simply no way to claim that 'the statistics are all over the map.' The statistics are actually now in a very small corner of the map."

Who makes false rape allegations?

Skeptics — including many police officers — tend to assume that false rape claims are made by women who had consensual sex but later regretted it, or who are trying to get back at a consensual sexual partner. According to the research, many police officers look for "red flags" that might reveal accusers' true motivation — cases where the accuser knew the accused, was intoxicated when the assault happened, waited several days (or longer) to report the assault, or wasn't injured or distressed.

But the evidence suggests that false rape claims tend to conform to the stereotype of violent rape — possibly because allegers think their claims will be more believable if they conform to that stereotype.

One study of false rape claims made to the Los Angeles Police Department and sheriff's department in 2008 found that 78 percent of false claims fit the definition of an "aggravated rape" — the accusers claimed the attacker had a gun or knife; that there was more than one attacker; or that she was injured during the attack. Forty-nine percent of false accusers claimed to have been raped by a stranger. And when it came to the circumstances of the alleged rape, false accusers were most likely to say it was an immediate attack or they'd been given a ride (or forced into the attacker's car). The standard "gray rape" scenarios, like being on a date or at a party or being assaulted while passed out, were cited by fewer than 20 percent of accusers.

Studies from outside the US also show that false accusations are more likely to follow those patterns, too. Those studies have shown that false accusers are disproportionately likely to say they were attacked by a stranger, and most of them file a report within 24 hours of the alleged incident. And furthermore, according to Lonsway, they're more likely to have a "clear and coherent" timeline of events.

78 percent of false claims fit the definition of an "aggravated rape"

So why do people make false accusations? The Los Angeles study suggested multiple reasons — including, for many accusers, mental health issues — but the most common reason by far was because they needed an alibi. Many of the false accusers identified in the Los Angeles study were teenagers who made up a rape allegation so they wouldn't get in trouble for breaking curfew. Others had cheated on their partners, and tried to cover up the infidelity by calling it rape.

Some accusers also filed rape claims out of a need for medical attention or sympathy. But the study's authors imply that it wasn't hard to tell when someone was making an allegation to get sympathy from the police or family. Many "had histories of making false reports, were described as known liars by family or friends, or explicitly stated they liked the attention they received as a result of reporting the rape."

Revenge wasn't a very common motivation. And regret or guilt — the motivation the "gray rape" narrative implies is most common — wasn't much of a factor at all.

Research about false reports to police, of course, doesn't necessarily tell us much about rape allegations made to other institutions, like university administrators. And that's where most of the skepticism of rape allegations is focused right now. But the reasons the skeptics give are the same reasons that police have given, since time immemorial, not to believe rape allegations: that rape is easily claimed and difficult to disprove, and that there are all too many possible motives to lie. And those affect their opinions of all victims: as one officer told the researchers who conducted the Los Angeles study, "We see so many women who aren‘t telling the truth that it affects our attitudes toward victims who are telling the truth. It makes us suspicious of all victims."

It's impossible to separate the public's conception of gray rape from the gray rape characteristics that police look for as evidence of falsehood — the two influence each other. And in the past, research that relied on police to record false rape accusations ended up codifying those assumptions, instead of checking them against the facts. The new body of independent research shows that those assumptions aren't based in reality — and that, to the contrary, they might be giving false accusers a script about how to lie.

The question is whether this research is going to get acknowledged, or if false accusations are going to continue to be treated as an unknowable X-factor in rape cases. It used to be a genuine mystery — but we now know a few things. We know that police tend to overestimate how many allegations are false, and we're moving toward a consensus about how frequent false allegations really are. We know that law enforcement officers have different attitudes toward sexual assault that shape how they pursue their cases, and we know that false allegations largely aren't driven by regrets after sex. And perhaps most importantly, we know how good data can be collected — and no longer have to rely on judgments about whether someone could "have removed (the victim's) extremely tight undergarments from her extremely large body against her will."

CORRECTION: This article originally stated that in the 2010 study of allegations at a Northeastern university, the rate of false allegations was found to be 6.8 percent. In fact, the study found that 8 of 136 cases were found to be based on false allegations — 5.9 percent. We apologize for the error.