False rape accusations are incredibly rare -- but most actual rapes are never even reported to police

Now that Brett Kavanaugh's accuser has come forward, the Supreme Court nominee's defenders have accused her of making up sexual assault allegations for partisan or personal gain.

But the reality is, only about 2 percent of all rape and other sex abuse charges turn out to be false, which is about the same rate as other felonies, according to FBI statistics.

One in six American women has been the victim of rape or attempted rape in her life, while about one in 33 American men have been victimized, and about 66 percent of victims are between the ages of 12-17 -- as Kavanaugh's accuser was at the time of the alleged attack.

Christine Blasey Ford claims she was assaulted 36 years ago at age 15 by a then-17-year-old Kavanaugh at a party, while his friend Mark Judge helped conceal the attack as it happened.

Conservatives have rushed to Kavanaugh's defense just days ahead of a vote to confirm him to the U.S. Supreme Court, saying Ford was making the allegations for personal gain or because she "had an axe to grind."

Both of those two alleged motivations fit into the four main categories -- which also include mental illness and a need for an alibi -- that explain false rape allegations, but those cases are far less common than popular imagination.

Only 52 men have had sexual assault convictions overturned since 1989 because they had been falsely accused, whereas 790 murder cases had resulted in exoneration due to phony allegations.

None of those 52 cases involved a so-called scorned woman out for revenge, although one man managed to convince his girlfriend to accuse a male roommate who had rejected his sexual advances.

Revenge cases generally tend to be convoluted and often involve jealousy, drugs, other criminal activity and sex for money.

For example, one woman accused a man of rape after she was disappointed with the amount of drugs she was given for sex, and an 18-year-old accused his older roommate after he refused to buy him a truck in exchange for sex.

Accusers motivated by personal gain sometimes make false claims to set up lawsuits, and those accusers tend to have histories of fraudulent claims against insurance companies, the government and business owners.

However, one woman lied about a rape in hopes of avoiding prison on drug charges, and one man who was already in prison made a false claim in hopes of being moved into a cell with his boyfriend.

Mental illness also plays a major role in false rape claims.

Some accusers have severe psychoses and sincerely believe they've been raped, but most mentally ill false accusers have personality disorders related to Munchausen’s syndrome.

Those accusers often make dramatic changes to their claims and make attempts to fake injuries or other evidence.

Other false accusations are made by teens in trouble with parents or by adults engaged in an affair, and they make the bogus claims in hopes of building an alibi.

The evidence suggests that charges in most false accusation cases are dropped before the accused even learns about the allegations against him -- while only about 40 percent of actual rapes are ever reported to police.