Jews, according to the stereotype, tend to be control freaks. We all crack jokes about our neurotic dads and balabooster mothers having Obsessive Compulsive Disorder.
But OCD is far from a joke, with an estimated 740,000 sufferers in Britain. And although not borne out by hard data, the clinical view is that Jews are more likely than the general population to be affected.
"There's always been a feeling that, like Catholics, Jews have a higher incidence of OCD," says Dr Roz Shafran, one of the country's leading researchers into the distressing condition.
Sometimes it takes the form of fearing one will cause harm inadvertently to one's nearest and dearest. But mostly, there is endless hand-washing, there is constant checking and there can also be a compulsion to count in a certain pattern - turning the light on and off precisely four times, for example, in an effort to ward off bad consequences in the same way as children avoiding cracks in the pavements.
Simply by looking at our history, it is easy to see why Jews are likely to become overly anxious, leading to obsessions and compulsions.
"In Judaism there are so many behaviours around washing hands, purity and morality, and given that OCD sufferers report that washing their hands repeatedly reinforces the problem, observant Jews are vulnerable," explains Shafran.
An even more common affliction of OCD sufferers than obsessive washing is the need constantly to check that doors are locked, taps turned off and irons are unplugged . "There are a lot of responsible Jewish mothers around," Shafran, herself a Jewish mother from Barnet, observes wryly.
As the need for this checking comes from an over-developed sense of responsibility, it is not hard to see why Jews are vulnerable to this behaviour. "Anxiety and conscientiousness can be a pretty toxic combination," she says.
One of the fascinating aspects about new research Shafran is doing in Reading is the discovery people may not be obsessed with washing because they feel physically dirty, but that they believe they may be contaminated mentally: "You can feel polluted as a person, just as a rape victim feels not only physically dirty but dirty again just remembering the rape."
In extreme cases, OCD sufferers can feel dirty just walking past a homeless person, or attending a funeral.
And it was another Jewish researcher, Professor Jack Rachman, who first exposed the idea that the feeling of being contaminated could emanate from something much less obvious than touching a dirty surface: "It seems logical now, but it took us all this time to make that connection."
Shafran even has a patient who believed that germs could jump from one surface to another: "Even though he knows that is not logical, he is terrified."
Surprisingly, perhaps, all religious people are vulnerable to a type of OCD involving blasphemy: "It is quite common to be standing in a synagogue and experiencing the unwelcome thought that God doesn't exist; Martin Luther King suffered those thoughts." The observant are also subject to a variation called scrupulosity - " an anxiety about always doing the right thing," explains Shafran.
The good news is that there is a treatment out there - about half of all OCD sufferers benefit from cognitive behaviour therapy (CBT). "It can be incredibly helpful, but people must make sure they are getting it from an accredited therapist," says Shafran, citing the British Association for Behavioural and Cognitive Pyschotherapies, or BABCP.
Its website lists therapists who are available on the NHS as well as
"It has become much easier to get access on the NHS, and, under a new service, people can refer themselves instead of having to go through their GPs," she adds. But some of our obsessions are perfectly logical, points out Shafran:
"You may fear that you are spreading salmonella when you wash out a chicken on a Friday. Scientists have confirmed that you can spread bacteria washing a chicken, so it's better not to do it- only cooking kills the germs ."
More information at www.ocduk.org.