Morningness–eveningness and intelligence among high-achieving US students: Night owls have higher GMAT scores than early morning types in a top-ranked MBA program

Individuals with a propensity to wake up early in the morning (“early-morning” types) and those who like to stay up late at night (“night owls”) often exhibit distinctive psychological and physiological profiles. Previous research has shown that night owls score higher than early-morning people on different measures of cognitive ability and academic achievement. Baseline cortisol is one of the physiological variables associated with variation in chronotype and cognitive function. In this study we investigated whether a relationship between chronotype and performance is present also in the high range of intellectual ability and academic achievement, namely, among graduate students in a top-ranked MBA program in the US. In addition, we measured baseline cortisol levels in saliva samples collected in the early afternoon and analyzed them in relation to chronotype and GMAT scores. As predicted, GMAT scores were significantly higher among night owls than among early-morning types, regardless of sex. GMAT scores were also significantly higher among men than women, regardless of chronotype. Morningness/eveningness was not significantly associated with variation in sleep amount or in undergraduate or graduate GPA scores, suggesting that the association between eveningness and high GMAT scores was not due to differences in study effort or skills. Sex, chronotype and baseline cortisol jointly accounted for 14% of the total variance in GMAT scores; baseline cortisol, however, did not mediate the effect of chronotype on GMAT scores. Consistent with the results of previous research, our study shows that the effects of chronotype on cognitive ability and academic performance are relatively small but detectable even among high-achieving individuals. The mechanism linking eveningness and high cognitive function remains unclear but the role of personality traits and neuroendocrine function warrants further investigation.