Dear Economist

PG mating

Dear Economist,

I am worried that if my children receive sex education at school, it will make unwanted pregnancies more likely. Should I take them out of class?

Protective Parent

Dear Protective Parent,

You are right to be worried. It is easy to see why information about contraception might encourage sex by lowering its costs, but the effects might be more dramatic than you would think. In a nutshell, fixed costs are your problem. These are obvious when it comes to, for instance, producing software. The first copy may cost hundreds of millions of dollars to produce, the second very little. But losing your virginity is like that too: the first sexual experience comes with a psychological cost, but, once paid, future experiences are easier. (Economics students will recognise the implication: sex has economies of scale, so it is efficient to either have lots or none at all.)

Within a relationship, too, the first sexual experience probably has a fixed cost.

In both cases, access to contraceptives makes it likelier that the first experience will be chosen; having crossed that barrier, it may become so attractive to have sex that teenagers will do so even when the contraceptives are not available.

The economists Peter Arcidiacono and Ahmed Khwaja, of Duke University, with Lijing Ouyang of the US Centers for Disease Control and Prevention, believe that this is the way teenagers do, indeed, behave.

Yet, I would not advise you to shield your children from sex education. That might be wise if prevention of pregnancy and disease were your goals, but that is too extreme. Your children will know that sex has benefits as well as costs. Perhaps you should refresh your memory about these?

Originally published at ft.com.