London, May 11 : Women in their late 30s are turning their backs on careers in science and technology and undermining key sectors of the economy due to a time warp of 1970s sexist attitudes, according to a new research.

Researchers claim to have discovered a "hidden brain drain" as women opt out when facing a choice between family life and pushing for promotion at work.

The majority choose their children and alternative careers instead of struggling with the hurdles of a macho "lab coat culture" with long hours, old boys' networks and the risk of sexual harassment.

Sylvia Ann Hewlett, an economist at the Center for Work-Life Policy in New York and the lead author of the study, said the research had revealed a world with values seemingly stuck in the 1970s.

"It has been a bit like a time warp. This predatory or condescending culture [towards women] was more common across the workplace 20 to 30 years ago but has somehow survived in an engineering, science and technology context," TimesOnline quoted Hewlett, as saying.

"It is the hidden brain drain. We have this amazing, talented pool of women who have left the industry. It is highly destructive to our society and economy," she added.

In Britain more than 225,000 science, engineering and technology (SET) graduates are not working in the industries for which they are qualified, and 50,000 of those are not working at all, according to official statistics.

The report claims the "sexist culture" persists despite concerns about dwindling numbers of female graduates staying the course.

Hewlett and her colleagues followed the careers of 1,000 women with SET qualifications in companies in America, and surveyed 3,000 staff employed internationally by three multinational companies. They also sought the opinions of women in cities including London, Palo Alto, New York and Shanghai in 28 focus groups.

The study, to be published in the Harvard Business Review, found that while women made up 41 percent of newly qualified technical staff, more than half dropped out by the time they reached their late thirties.

Nearly two-thirds of all women surveyed said they had been victims of sexual harassment in the workplace. A similar number objected to the "lab coat culture", in which researchers laboured over experiments, "tethered to the microscope", for up to 12 hours a day.