High birthrates among the ultra-Orthodox are responsible for a recent growth in the number of British Jews following decades of decline, a new study shows.

The trend was featured in a report published Thursday by the Institute for Jewish Policy Research, or JPR, and the Board of Deputies of British Jews.

According to “Vital statistics of the UK Jewish population: Births and deaths,” births in the British Jewish community have exceeded deaths every year since 2006. Other things being equal, the report’s author wrote, this implies “Jewish demographic growth in the United Kingdom.”

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As ultra-Orthodox Jews elevated the average overall for the Jewish community since 1979 — their birthrate is estimated at seven children per woman — the number of deaths within that group decreased noticeably in the same period in connection with improvement in health services and life expectancy.

From 1979 to 2006, the United Kingdom saw an average of 3,165 Jewish births and 3,858 Jewish deaths, according to the study. But in the years 2007 to 2015, the average figures were 3,599 and 3,254, respectively.

“The high fertility rates among the Haredi (ultra-Orthodox) sector are the main reason why we observe the positive natural increase of the Jewish population in the UK since 2006,” the report states. Ultra-Orthodox Jews are a growing minority in British Jewry. In 2015, ultra-Orthodox births accounted for 47 percent of all Jewish births, the report’s authors estimate.

The mainstream Jewish birthrate in the United Kingdom is 1.98 children per woman, only slightly above the national average. But combined with the ultra-Orthodox community, the total Jewish birthrate in Britain is 2.6 per woman.

A JPR report from 2015 said Britain’s ultra-Orthodox community is increasing by nearly 5% a year while the wider, non-Haredi Jewish population is decreasing by 0.3%. Members of the ultra-Orthodox community are projected to make up half of all Jewish children aged 0–4 years within British Jewry by 2031, according to the 2015 report.

The United Kingdom now has about 250,000 Jews, according to the European Jewish Congress.

Government authorities in the United Kingdom do not register religion at birth or death. The latest report used various sources to reach its estimates, including surveys and data from circumcisions. The researchers extrapolated from that data to account for female births “assuming that Jewish birth sex ratios are identical to those in the general population,” the authors wrote.