A team of psychologists led by a woman has uncovered some surprising findings on one of the most secret aspects of female sexual fantasy.

While almost everyone has sexual fantasies, previous research into the subject has found between 31 and 62% of women have rape fantasies. To be sexually aroused by such an imagined scenario represents a psychological mystery. Why fantasise about a criminal act which in reality is repulsive and harrowing?

To investigate these and other riddles at the heart of female erotic fantasy, a team of researchers based at the University of North Texas and the University of Notre Dame studied 355 young women.

A part of the research involved the participants being read a rape fantasy scenario over headphones, to investigate how aroused they became.

In the study, published in the academic journal Archives of Sexual Behaviour, participants were instructed to close their eyes while listening and to try to imagine themselves as the woman described in the narrative. This scenario was derived from story lines typically found in much women's romance literature, so it portrayed an erotic rape fantasy, rather than a literal portrayal of actual assault.

This was the scenario: a male acquaintance is strongly attracted to the female character. He expresses a yearning for sex with her, but she's clearly unresponsive. He attempts without success to convince her. When she continues to openly refuse, he overpowers and rapes her.

The female character is resistant throughout the interaction and at no time gives consent. However, as the man is attractive and he provides erotic stimulation, she does experience gratification from the forced sex. The scenario places more emphasis on the use of coercion than on the sexual pleasure.

The results of the study, (which also explored other sexual and aggressive fantasies, self esteem, attitudes to sex and other personality testing) are that 52% of the women had fantasies about forced sex by a man: 32% had fantasies about being raped by a man: 28% - forced oral sex by a man: 16% - forced anal sex: 24% - incapacitated: 17% - forced sex by a woman: 9% - raped by a woman: 9% - forced oral sex by a woman. Overall, 62% reported having had at least one of these fantasies.

The team of researchers lead by Dr Jenny Bivona, based at the University of North Texas found that overall, 62% of participants reported having a rape fantasy of some type.

Of the women who reported having the most common rape fantasy rape fantasy, ''being overpowered or forced by a man to surrender sexually against my will,'' 40% had it at least once a month and 20% had it at least once a week. The authors conclude these results indicate rape fantasies play a significant role in the sexual fantasy lives of many women.

It's important to note that while headline writers may focus on the fact women have sexual fantasies about coercive sex, this research finds it's an occasional daydream, not a preoccupation. It would be similarly unfair to tar men with the brush of an occasional fantasy they may have. When these female fantasies are erotic in character, the male protagonist is always described as highly attractive or otherwise desirable.

According to this study, entitled Women's Rape Fantasies: An Empirical Evaluation of the Major Explanations, a previous common psychological theory as to why women should fantasise about rape or forced sex was termed 'sexual blame avoidance'. This theory was about women avoiding taking responsibility for sexual desires. The hypothesis argued that women have been socialised by our culture to work hard at not being perceived as promiscuous or overly sexual. For example, stigmatising labels, such as ''tramp'' and ''slut,'' are invoked which control or restrict female sexuality.

'Sexual blame avoidance' theory argues that, for some women therefore, fantasies of consensual sex could generate self-blame, guilt, and anxiety. So by letting the fantasy take the form of rape, the woman in the fantasy is being forced to do something she doesn't want to. It follows then she can't be blamed for the occurrence of sex. In contrast to a consensual sexual fantasy, a forced sex theme enhances sexual gratification by allowing the fantasiser to avoid blame and guilt.

The results of this study found no support for this theory.

The authors of this new ground-breaking research concede that 'sexual blame avoidance' may have been true in the past when we lived in more sexually repressed times, so it's possible that over recent decades changes in attitudes to sex means the stress for women of being viewed as overly sexual has disappeared. Now few women appear to have rape fantasies to avoid blame from having openly consensual sexual fantasies.

In direct contrast to 'sexual blame avoidance', is the 'openness to sexual experience' theory. Instead of being driven by repressed sexuality, this supposition is rape fantasies derive from a generally open, tolerant and guilt-free attitude toward sex. It was this theory which received the strongest support in this new research by Dr Bivona and colleagues.

A notable finding is that women who reported being less repressed about sex were more likely to have rape fantasies, but were also more open to fantasy in general, more likely to have consensual fantasies, and more likely to report a higher level of arousal to rape fantasies.

Interestingly, the women who reported having frequent rape fantasies were also likely to report having fantasies about "overpowering or forcing a man to surrender sexually against his will."

Fantasising about being a stripper also predicted a tendency to fantasise about rape. Another intriguing result is women who report rape fantasies were more likely to have high self-esteem.

These results suggest that having fantasies about things we would never endorse or choose to do in reality, are not necessarily signs of psychological disturbance. In fact, according to this research, women who have rape fantasies also tend to have more positive attitudes toward sex, high self esteem, and more frequent consensual sexual fantasies.

This study in no way condones or tries to justify rape, which remains a violent and reprehensible crime no matter what the research on sexual fantasy of either gender might turn up. While some may even believe that publishing results such as these is going to assist some rapists in justifying their actions, the reality is these violent criminals are not scanning erudite academic research searching for justifications for assault. The editors and armies of academics who consider research submitted for publication in academic journals such as Archives of Sexual Behaviour also clearly believe this kind of study deserves publication, and wider dissemination in the field.

Fantasy is a deeply problematic area for many people and for psychiatry and psychology - why do some people convert strange ideas into actual deeds - as in the case of Brievik the Norway mass murder scenario - while others just enjoy their vivid, creative and somewhat unusual imaginations without taking action. Why do various individuals become disturbed about fantasies of which they don't approve? As a result much psychosexual therapy involves exploring and confronting the mysteries of sexual fantasy.

We don't yet know the answers to many of these questions, but this kind of scientific investigation is assisting in our search for understanding.

Dr Raj Persaud is a Consultant Psychiatrist based in London, Dr Jenny Bivona graduated from the University of North Texas and now works as a clinical psychologist.