Good news! Well, sort of: The United States’ teen birth rate has hit an all-time low -- but it is still double that of 20 other industrialized nations. Economists are trying to understand why.

First, the good news: In 2010, the most recent year for which data is available, there were 34.4 births per 1,000 U.S. women ages 15 to 19., a 9 percent drop from the year before, according to a report from the Centers for Disease Control and Prevention. American teen birth rates fell across all age and racial groups that year, indicating a widespread trend.

(The Center for Disease Control)

This an especially welcome development after the rate ticked upwards in the mid-2000s, leaving researchers wondering whether the big reductions in the 1980s and 1990s (in the chart above) were about to be reversed.

Now, the bad news: America’s teen birth rate dwarfs that of the other industrialized nations that were measured.

(National Bureau of Economic Research)

A teenage girl who grows up in the United States is nine times as likely to give birth as one who grows up in Switzerland and twice as likely as someone who grows up in any of the 19 other industrialized countries in the report. Why? Blame income inequality.

In a new working paper, Kearney and Levine looked at international differences in birth rates, as well as variations among American states. There are widespread differences in rates: New Hampshire’s stands at 16.4 births per 1,000 teens, while Mississippi’s is 64.4. The researchers found a state’s level of economic inequality to be a significant influence in the birth rates. All other things being equal, “teens in the highest-inequality states are roughly 5 percentage points more likely to give birth as teens in the lowest-inequality states,” Kearney and Levine wrote. This was true even when the researchers controlled for the individual teenager’s economic status.

“We conclude that women with low socioeconomic status have more teen, nonmarital births when they live in higher-inequality locations, all else equal,” they said. “Our estimates suggest that income inequality can explain a sizable share of the geographic variation observed in the teen childbearing rate, on the order of 10 to 50 percent...To the extent that greater levels of inequality are associated with a heightened sense of economic despair and marginalization, our empirical findings support this claim.”

That economic inequality can produce high teen birth rates would align with what we know about disparities in wealth here and abroad. The World Bank has consistently found a greater level of economic inequality in the United States than in Europe.

Some other factors may also be behind the discrepancy. American teens tend to have intercourse at lower rates than some of their international counterparts, yet they are also less likely to use contraceptives. About one-third of American teens terminate their pregnancies, which is an abortion rate similar to that of Germany (31.3 percent) but slightly lower than other countries, such as the United Kingdom (38.8 percent).