While the question is not dumb, the answer is in the very first sentence of the link. So aking the question here is, yes, dumb.
I know nobody read the links anymore and react only to the title but, seriously, that’s worrying to not even try when you have a question. Writing the question to ask probably took 10 times more than clicking on the link and reading the first sentence.
"Read the paper" isn't exactly the answer I'm looking for, but thanks for trying.
Only upon reading the paper do you discover that a "school-age cutoff", much like the famous hockey player study cited by Gladwell in Outliers, is one of the ways for controlling the selection effect I mention.
I know nobody read the links anymore and react only to the title but, seriously, that’s worrying to not even try when you have a question. Writing the question to ask probably took 10 times more than clicking on the link and reading the first sentence.