What, more than 17 million patients couldn't have told them this? Sigh. I think we need studies in adults too, with controls matched for age and other factors.
Remember that the opinion or thoughts of the patient are only worth to bulk up a psychiatric/psychological recommendation and rarely to cause research of actual physical deterioration or illness. Any idiot can conclude that an illness that screws up sleep/and or is obviously affecting the CNS because of symptomatology will make the patient dumber, but scientists often "need" evidence of the obvious. I find these kind of studies useful nonetheless, because people DO need proof of the obvious, because they bathe in wishful ignorance and lack of empathy.