We sometimes assume that ingrained social problems are just that – ingrained. At best we can only whittle away at them slowly and at considerable expense.

And yet one can find examples to show that rapid progress isn’t just possible, but is already happening. In an encouraging and intriguing piece for Vox, Sarah Kliff investigates the remarkable decline in teenage pregnancy rates across America:

“For five years now, America’s teen birth rate has plummeted at an unprecedented rate, falling faster and faster. Between 2007 and 2013, the number of babies born to teens annually fell by 38.4 percent, according to research firm Demographic Intelligence.”

What could explain this? For a start, not abortion:

“This drop occurred in tandem with steep declines in the abortion rate. That suggests that the drop isn’t the product of more teenagers terminating pregnancies. More simply, fewer girls are getting pregnant.”

The sudden declines coincides with the steepest economic downturn since in living memory, so an economic explanation would seem reasonable:

“But here’s what the recession doesn’t explain: why the number of teen births fell more than four times faster than the overall birth rate during the 2007 to 2013 period.”

Kliff argues that, if anything, one would expect the family planning response to the recession to be stronger among older parents.

Other explanations include more effective use of contraception, but again that doesn’t seem to fit the facts very well:

“…an increasing number of adolescents use no contraceptives at all. In 2013, 13.7 percent of sexually active high school students reported not using any protection, up from 11.9 in 2009, according to the federal government’s Youth Risk Behavior Surveillance System.”

What about sex education? A variety of approaches are used in America, so might the reduction in pregnancy rates be explained by some of the more successful programmes? This may be true in some areas, but it’s hard to see how localised innovation can account for such a significant, sudden and widespread improvement.

Perhaps what we need is a cultural explanation – which is why there’s been a lot of interest in the influence of TV shows that present a realistic portrayal of life as a teenage mother. There’s some evidence to suggest that these have had an impact, but not enough to explain the overall and continuing downward trend.

Kliff’s article is focused on America, but it’s interesting that the latest statistics show an extremely rapid decline in teenage pregnancy rates in Britain too. Furthermore, this has taken place over the same period – i.e. it coincides with the debt crisis and its aftermath.

I would therefore return to an economic factor as the most likely cause – but one that explains why the impact has been particularly strong on teenagers.

It’s striking that while young people today are more socially liberal than older generations, they are notably less accepting of the idea of welfare dependency. A generational shift towards a culture of self-reliance is not exactly compatible with teenage motherhood.

Previous generations of teenagers will have grown up in a time of expanding welfare provision and a seemingly endless supply of borrowed money with which to pay for it. However, for the current generation the outlook is dramatically different. It would surprising if this didn’t result in a correspondingly different pattern of behaviour.