Statistics, sex, and grades

15Aug10

I’ve talked about how statistics can be seductive and suggestive, but utterly misleading. Another example cropped up in the news today a study correlating teenage sexuality with grades (link). The claim is basically this – teenagers who have casual sex have lower grades and have more problems in school.

So, how worse are the grades? About 0.13 GPA for girls and 0.3 GPA for guys. So, let’s say, quarter of a point. Does this matter?

I think that depends on the starting grade. If you’re 0.1 point short of a 4.0 GPA, that might be something important, since it keeps you from being a valedictorian. But is there a difference between 3.0 and 3.2? I don’t think so. At this point, other things, such as standardized tests and extra-curricular activities would make the biggest difference in how the student is perceived. Students with GPA scores of 3.0 and 3.2 are, academically, basically identical.

Figures on school delinquency and detention rates were not provided in the article.

Then we get to the best, and classic part – utter confusion about causality and correlation.

In a statement, the Family Research Council said the study confirms what the group has long advocated about the negative consequences of casual sex.

The study highlights that both things – a slightly lower GPA and casual sex – happen at the same time. This doesn’t mean that one causes the other. One could claim that casual sex causes students to do worse in school, by being a distraction, for example. One could also claim that lower grades cause students to drown their sorrows in promiscuity. Both suppositions are equally weak.

I would hypothesize that other factors – such as personality traits or family conditions, for example – pre-dispose these teenagers to seek the instant gratification of casual sex over the drawn-out and obscure reward structure of schooling.

I would further hypothesize that people jumping to conclusions as FRC has also didn’t pay attention in school, but probably due to things far less exciting than casual sex.

PS I’m trying to find the original study, but can’t track it down at the moment. If I do find it, I might write more about it.

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Tags: high school, sex, statistics