Sigh. BYU Economics professors do a "study" that shows that kids that get 7 hours of sleep are smarter than kids that get 9, and then try to say that perhaps kids don't need any more than 7 hours of sleep a night.
Correlation is not causation, and asking kids to self-report hours slept is not exactly good science. This is why Economics professors shouldn't do science.
I know quite a few people who know a lot more about science and sleep than I do (I did, after all, work as an underling at what is probably the top sleep lab and the top sleep research lab in the world), but even I could come up with a vastly superior way to figure out how the amount of sleep a kid gets affects performance.
First: Take 100 teenagers of similar age. Pick 50 at random for each group (getting a good mix of gender, race, etc. in each group). Test them for response times, performance on tests, etc., and for sleeping disorders. Eliminate any with sleeping disorders. Then place them in a controlled environment for a month. Have 50 of them spend 9 hours a night in bed, and have 50 of them spend just 7 hours in bed. Evaluate their sleeping patterns to see how long they actually sleep. During the day time, run various performance tests. How do individuals do, over time, in each group? Do they improve or get worse? By how much?
The difference between the above experiment and the "study" done by the BYU Economics professors? The above experiment is an actual study, and its results would actually mean something. We don't expect science professors to do study on Economics. Economics professors certainly have no place trying to run a scientific study (although it's rather hilarious how poorly they do).
To be fair, one of the economists, Showalter, at least recognizes some of the weaknesses in the study. The other economist, however, seems to be entirely clueless.
Please, next time leave the science to the actual experts...