The meaning of group differences in cognitive test performance

What does it mean that groups of individuals given a diagnosis of schizophrenia get fewer items correct and respond more slowly than comparison groups on tests of memory, attention, executive functioning, and social cognition? Green et al's answer1 is unequivocal: the weaker performance is caused by a “cognitive impairment”？, which is a “primary deficit”？, arising from a specific neuropathological cause. This “im‐pairment” is viewed as both a vulnerability factor and a “core feature” of schizophrenia. This is a position currently held by a majority of the field and supported by a large evidence base