The number of American Jews who regard themselves as culturally rather than religiously Jewish has almost doubled in a decade, according to new research.

American Jews who identify by ethnicity have increased from 20 per cent to 37 per cent of the American Jewish population since 1990, while the proportion of those who follow any of the streams of Judaism has dropped by more than a fifth in the same period.

Barry Kosmin and Ariela Keysar, of Trinity College, Hartford, Connecticut, the authors of the American Religious Identification Survey 2008, presented their findings at a conference in Jerusalem last week.

Professor Kosmin, a former director of the Institute for Jewish Policy Research in London, reported: “Though the total Jewish population is relatively stable in size, disaffection from Judaism and intermarriage have combined to change the identity profile of American Jewry in the past 20 years.”

He explained: “Since 1990, half of all marrying American Jews have married non-Jews, with the result that there are two new mixed households for every homogeneous Jewish one.”

The figures suggest that “the Jewish population is further ahead in the process of secularisation than Americans in general”.

“Over half of American Jews claim they have a secular outlook,” Ms Keysar said. “Most of them see no contradiction between adhering to a religion and having a secular orientation.”

The ARIS study, based on a sample of more than 54,000 adults, found that secularism was increasing among Americans generally. Whereas just over eight per cent said they had no religion in 1990, that figure had almost doubled by 2008 to 15 per cent.

The number of religiously identifying Jews had dropped from 1.8 per cent of the American population in 1990 to just 1.2 per cent last year.

Jews are among the mostly highly educated religious group , with 57 per cent over the age of 25 graduates, compared with a national American average of 27 per cent. The most educated group are those of Eastern religions with 59 per cent graduates.

Seventy per cent of Americans say they believe in a personal God, another 12 per cent in some sort of higher power and 12 per cent are agnostic or atheist.

While the core American Jewish population, ethnic or religious, was estimated at around 5.34 million in 2001, Professor Kosmin said the extended Jewish population in the USA including all those who would be eligible to settle in Israel under the Law of Return could be more than 10 million today. However, many adults with a Jewish mother followed another religion, overwhelmingly Christianity.