Belief in God is highest among older people and increases with age, perhaps due to the growing realization that death is coming closer, University of Chicago researchers said on Wednesday.

Summarizing data from surveys performed in 1991, 1998 and 2008 in 30 countries from Chile to Japan, the university’s National Opinion Research Center found that, on average, 43% of those aged 68 and older were certain that God exists.

By comparison, an average of 23% of people aged 27 and younger were firm believers in God, according to the report, which gathered data from the International Social Survey Program, a consortium of the world’s leading opinion survey organizations.

“Looking at differences among age groups, the largest increases in belief in God most often occur among those 58 years of age and older. This suggests that belief in God is especially likely to increase among the oldest groups, perhaps in response to the increasing anticipation of mortality,” researcher Tom Smith said in a statement.

Over the past two decades, belief in God has decreased in most countries, but the declines were modest, Smith said.

Israel, Slovenia and Russia were three exceptions where belief in God had grown. For instance in Russia, non-believers who became believers outnumbered by 16 percent those who had lost their belief in God.

Belief was highest in strongly Catholic countries such as the Philippines, at 94%, and lowest in Western Europe, with only 13% of former East Germans believers.

In the United States, 81% of people surveyed said they had always believed in God, and 68% support the concept that God is concerned with people in a personal way.

People were asked about their range of beliefs, from atheism to strong belief in God; their changing beliefs over their lifetimes; and their attitudes toward the notion that God is concerned with individuals.

The countries surveyed were Australia, Austria, Chile, Cyprus, Czech Republic, Denmark, France, Germany, Britain, Hungary, Ireland, Israel, Italy, Japan, Latvia, The Netherlands, New Zealand, Northern Ireland, Norway, The Philippines, Poland, Portugal, Russia, Slovakia, Slovenia, Spain, Sweden, Switzerland, and the United States.