(RNS) The number of American Jewish households that affiliate with aJewish congregation has increased by 15 percent since 1990, even as the"core Jewish" population declines, reports a new demographic survey.

According to the American Jewish Identity Survey 2001, which wasconducted by the Center for Jewish Studies at the Graduate Center of theCity University of New York, 1 million households affiliate with acongregation; this is up from 880,000 households a decade ago.

Another 1 million Jews report they are affiliated with anoncongregational organization, such as a Jewish community center.

At the same time, the number of "core Jews" -- people whoconsider themselves Jewish by parentage or upbringing, but do notnecessarily practice Judaism -- has declined from 5.5 million to 5.3 million people.

And the number of people who are of Jewish parentage but who identify themselves as members of other religions, a subcategory of people not counted within the core Jew rubric, has increased from 625,000 to nearly 1.5 million.

Multiple factors, including intermarriage, were cited as the reasonfor these changes. Even though the rate of intermarriage, 51 percent, hasremained steady over the past decade, the study's authors noticed anincrease of "core Jews" who intermarry -- 33 percent, up from 28 percentin 1990.

The Reform movement, which reaches out to intermarried families moreactively than Conservative or Orthodox communities, has benefited mostfrom the affiliation increase. In 1990, 35 percent of affiliatedhouseholds were Reform; the study found that in 2001, that number hadincreased to 41 percent.

The study, which was based on a random sampling of 1,668 Jews,replicated some methodology and questions from the larger NationalJewish Population Survey 1990.