Big Planet

More sex is safer sex

In popular economics on July 24, 2009 at 10:06 am

The key to reducing the risk of sexually transmitted diseases is not lesser sex, but more sex. This is according to Steven Landsburg, a professor of economics who writes columns at Slate in the tradition of Levitt and Dubner’s Freakonomics and Tim Harford’s The Undercover Economist. He is also the author of More Sex is Safer Sex. For him, the AIDS epidemic is not worsened by promiscuity, but rather by monogamy, chastity and sexual conservatism.

I like the thinking style of Landsburg because he shows that what we think as common sense is in fact irrational. His solutions to social problems, like urban congestion, are often the reverse of our assumptions of correctness. His rhetorical skills show this pattern: “X, which is thought to improve Y, actually worsens it”. Here are some of his claims in the past, backed by economic theory applied on everyday life:

1. Parking your car is more environmentally destructive than driving it.
2. We shouldn’t aid Katrina’s victims too much.
3. Pornography prevents rape.
4. It makes more sense to play the lottery than to vote during elections.

He talks about the economics of faking orgasms. He applies the marginal analysis in discussing why people stand still on escalators but not on normal stairs. Tim Harford praised Lansburg for his unconvential wisdom. The meaning of “unconvential” in his case is his ability to attack popular assumptions.

In More Sex is Safer Sex, he argues that conservatism, chastity and monogamy help spread epidemic, and claims that increased sexual activity can help reduce the risk of AIDS. The argument runs thus:

Identifying key players. One, we have a person who is looking for sex. Two, we have a set of potential partners. We divide this set into two groups: the promiscuous ones and the conservatives.

Quantifying the risk of getting HIV. Now let’s say you’re looking for sex in a party. You spot four (4) potential partners. Let’s say two (2) of them are promiscuous (engaging in casual sex, sleeping with strangers or with more than one partner or husband, etc.), and the rest are conservative (either  monogamous, virgins, or just cautious and picky).

Since the promiscuous group is more likely to be HIV positive, and the set is divided into two equal groups, there is 50% chance of getting an unsafe match. Supposing, however, that the conservative crowd in the general population doubles the frequency of their sexual activity (e.g. instead of getting sex just once a year with a partner met in a party, they now have sex twice), you will find that their number in the set increases. Hence, when you step into a party, you are more likely to add two (2) more conservatives in the set of potential partners. Now you have six (6) potential partners, four (4) of which are conservatives and only two (2) are promiscuous.

This means the risk of having unsafe sex is now just 2/6 or 33%, and the chance of sleeping with a safe partner is 4/6 or 67%. That is why we say that more sex reduces the risk of AIDS because the probability of having sex with an HIV-positive partner is reduced from 50% to 33% given that the conservative crowd in the general population becomes more sexually active.

Landsburg’s advice: let the sexual conservatives have more sex. It’s more doable than preaching sexual conservatism to the promiscuous crowd.

The solution isn’t that simple if we put monogamy into the equation. I’ll save this for my next post, The Market for Prostitution.

Related posts:
Reincarnation Bank
Economics and Global Climate Change

  1. […] The market for prostitution In Uncategorized on July 24, 2009 at 10:38 am (This post is a continuation of More Sex is Safer Sex). […]

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