Am I missing something? This study just seems to say that smarter people have more income stability. Doesn't seem all that surprising. The study doesn't make

Am I missing something? This study just seems to say that smarter people have more income stability. Doesn't seem all that surprising. The study doesn't make any mention of doing tests throughout their lifespans so it's hard to claim that income stability impairs brain function. At best there is a correlation and it makes more sense to me that impaired brain function leads to income instability, not the other way around.