Economics might not be the most obvious discipline for studying teenage sexual activity and its results, but the dismal science can, in fact, throw some light on what seems an intractable modern problem.  

UK professor of industrial economics, David Paton, has done that in an article in the British journal Education and Health. His comparison of government policy interventions and underage conceptions in England and Wales over the past 40 years shows very little net effect. The rate of conceptions to under-16s in the two countries was almost exactly the same in 2009 as it was in 1969.

There have been ups and downs in the rate (the original has graphs, which are helpful), but they do not neatly correspond to major government initiatives to “cut teenage pregnancy” or to the gaps between.

Notably, the decrease in underage pregnancy that has occurred since the late 1990s stems largely from a decrease in underage births. In contrast, the rate of underage conceptions ending in abortion (probably the best measure of unwanted pregnancy) appears to have been particularly resistant to policy interventions, with the rate in 2009 being higher than at the start of the 1999 [Teenage Pregnancy] Strategy.”

Dr Paton points out that government policies in this area have centred on school-based sex education and access to family planning (contraception) -- on the assumption that such measures will reduce pregnancy rates amongst teenagers already having sex but will not cause others to begin sexual activity. And here is where the economic theory comes in:

“Standard economic models, however, suggest that the two factors are irretrievably interlinked. Easier access to family planning reduces the effective cost of sexual activity and will make it more likely (at least for some teenagers) that they will engage in underage sexual activity.”

This is also known as “risk compensation” -- if a behaviour suddenly seems less risky or “costly” (because “I am on the pill”) there will be more of it, or if one type of risk is reduced people will take other risks. And yet, as Paton notes, teenagers do not use contraception consistently, so it is impossible to predict how much risk will be reduced by greater “access” to the pill and condoms, and what the cost will actually be. Retrospectively, the evidence is not convincing.

A study published last year found that parts of the UK promoting emergency birth control (EBR) did not experience bigger reductions in underage conceptions than other, similar areas. But they did have more young teens with STIs, says Paton.

“Indeed, not a single peer-reviewed study to date has found that access to EBC has led to a statistically significant reduction in unwanted pregnancy or abortion rates…”

Ah, but that’s because we don’t have good, comprehensive sex education early enough in schools (SRE as they call it in the UK) as they do in the Netherlands, say the enthusiasts.

Sorry, says Paton, but the peer-reviewed evidence on the impact of SRE on pregnancy rates in the UK is weak, at best. And cross-country comparisons present a mixed picture.

“Contrary to common perception, school SRE in the Netherlands (where underage abortion rates are indeed significantly lower than in the UK) is compulsory at a later stage than in the UK and, as in the UK, there is no uniform or statutory SRE content…”

What does appear to work overseas, says Paton, is parent involvement in the sexual health decisions of minors, especially abortion.

“US states that have introduced mandatory parental involvement laws have not only seen relative decreases in abortions to minors … but also a reduction in teenage STIs … and improvements in teenage mental health …”

The time appears ripe, says Paton, for a shift of emphasis in the UK from reducing the risks associated with teenage sexual activity to aiming more directly at reducing the amount of sexual activity. 

Which is plain common sense, but it is up against so-called sexual health organisations that really believe teenagers can "enjoy their sexuality without harm" if only they have enough information.