Bad Stats
The latest issue of Time magazine exemplifies the exact sort of idiocy that would have my AP Statistics teacher coughing up hairballs - they confuse correlation with causation.
The article at blame is titled “Why Girls Need Gym Class: Physical fitness has tangible effects on classroom performance, says a new study”. However, despite the author’s assumably confident interpretation, the study says nothing of the sort.
The study says that, out of a few thousand students surveyed, girls who got a significant amount of physical education each week scored significantly higher on standarized tests. However, the study never mentions any kind of controlled experiment that would lead one to conclude that the physical education CAUSES the higher test scores. It just states that a correlation has been found.
Curiously, boys’ test scores are apparently unaffected by gym class, assumably because they get more exercise outside of school than girls do. However…this is simply not true anymore. The students surveyed in the study were all elementary school, and it seems to me that elementary school is when both genders get precisely the SAME amount of exercise–it is only in later grades that boys get into school sports (many of which girls don’t participate in, such as football and wrestling), and girls get into doing their hair and watching cute boys play football and wrestle.
But besides this strange anomaly, the main point I want to make is this: hasn’t it occured to anyone that perhaps there’s a different reason for physical education to be linked with standarized test performance?
For instance, students at such a young age are very susceptible to how they are being educated. I’m in high school and I can educate myself - I read books and magazines, look up stuff online, talk to adults who (hopefully) know what they’re talking about, analyze things and write blog posts, etc. Younger kids, however, usually only learn what they’re taught at school. The sort of school system that offers its students gym class is likely to be more financially endowed, more respectable, BETTER than a school system that doesn’t. A better school, in the elementary grades especially, may often translate to better test scores.
And that’s just one example.
Another thing to note is that the article doesn’t mention if these kids are public school students only, or if private and parochial schools are included. That makes a difference.
And, finally, the study was carried out by the Centers for Disease Control. You’d think they’d WANT to promote exercise anyway.
The article concludes with a typical bashing of No Child Left Behind (not that I disagree with it on this), and states, “…most kids have gym class only once or twice a week. That lack of physical exercise could be adversely affecting girls’ academic development.”
Well. At least they used the word “could”.
~Mimzy
Nice writeup, and I think you’re right about this. Time magazine tends to be like all the other news writing agencies out there, though–given to sensationalism.
One thing that should be pointed out is that as we increase the number of days per year that students attend school, the less likely they’re going to have time or want to play outside of school. School can take up a lot of time. So either we need to stop making kids go to school so many days out of the year or the burden will have to be shifted more to educational centers to provide school-hour physical education. I personal thing the former is better, but everyone is convinced that grades go up the more kids are at school (not true), so that won’t be happening.
Another thing that should be paid attention to is not a possible correlation between physical education and grades, but a possible correlation between “breaks” and grades. I firmly believe that if you place students in drab classes all the time, they’re going to be less interested in learning after a certain amount of time. The break afforded to these students, through the physical education, is possibly the reason the grades changed. The same thing might have occurred with the addition of an arts or music class.
Sounds like this was a truly bad study, as well as a bad article on it. As you pointed out, information about their sampling is very important, despite its not being given. I’d like to know what the change in grades actually was. If it was a few points, that could easily just be coincidence (i.e., students were calmer about taking a test the second time around). If it was 10 or more points, then that’s significant. Otherwise, it’s all up in the air, isn’t it?
Nice catch.