LONDON - Death rates in children under 5 are dropping in many countries at a surprisingly fast pace, according to a new study that estimates far fewer children are dying every year than the United Nations previously guessed.

Using more data and an improved model, scientists predicted 7.7 million children under 5 would die this year, down from nearly 12 million in 1990. The study was published online Monday in the British medical journal Lancet.

UNICEF's last estimate, in 2008, said about 8.7 million children died every year of preventable causes such as diarrhea, pneumonia, and malaria.

"We're quite a bit farther ahead than we thought," said Christopher Murray, one of the paper's authors and director of the Institute for Health Metrics and Evaluation at the University of Washington.

Murray and colleagues assessed information from 187 countries from 1970 to 2009. They found child deaths dropped about 2 percent every year.

Murray said death rates were falling surprisingly fast in poorer countries including Liberia and Niger, but that progress had stalled in rich countries like Britain and the United States. The study was funded by the Bill and Melinda Gates Foundation.

"We're very excited because this study reinforces our belief that the scale-up of interventions such as [malaria] bed nets, vaccines, and vitamin A [pills] are starting to show an impact," said Mickey Chopra, director of health for UNICEF, which was not involved with the study.

But global health figures often fluctuate.

There was also no evidence to show that U.N. programs are responsible for the drop. Murray said the reduction could be because the AIDS epidemic peaked several years ago.