An overwhelming amount of research has indicated that evening-types report more negative psychosocial functioning as well as more negative sleep characteristics (e.g. more sleep problems) relative to morning-types. Researchers also find a strong, consistent link between poor sleep characteristics and negative psychosocial functioning. These studies, however, have been based on a variable-centred approach, and thus were not able to assess possible individual differences within morning-types and evening-types with respect to their sleep characteristics prior to assessing differences in psychosocial functioning. Thus, it is not clear whether it is morningness-eveningness per se or sleep characteristics that explain the differences in psychosocial functioning found between morning-types and evening-types. The purpose of the present two-year longitudinal study was to employ a person-centred approach to determine whether there are subgroups within morning-types and evening-types based on 10-sleep characteristics (e.g. sleep problems and sleep duration). Then subgroups were compared on three indices of psychosocial functioning (i.e. academics, intrapersonal adjustment and alcohol consumption), both concurrently, as well as one year later. Participants were 780 (72.2% female; M = 19.0 years, SD = 0.90) emerging adults at a mid-sized university in Southern Ontario, who were either morning-types or evening-types. A latent class analysis (LCA) conducted for morning-types yielded two subgroups, classified as having good sleep characteristics (i.e. morning-good) and poor sleep characteristics (i.e. morning-poor). Results of a second LCA conducted for evening-types yielded three subgroups, classified as having good (i.e. evening-good), moderate (i.e. evening-moderate) and poor (i.e. evening-poor) sleep characteristics. Results comparing subgroups across the 10-sleep characteristics indicated that morning-good and evening-good individuals reported very similar scores, and both were characterized by the least sleep problems and longest sleep duration relative to the other subgroups. In terms of the three psychosocial functioning indices we found that academic achievement generally did not differ across the five subgroups (i.e. morning-good, morning-poor, evening-good, evening-moderate and evening-poor). With respect to intrapersonal adjustment, morning-good and evening-good subgroups reported significantly better intrapersonal adjustment relative to the other subgroups across time. Interestingly, evening-type subgroups generally reported higher alcohol consumption than morning-type subgroups. Overall, these results suggest that intrapersonal adjustment in particular appears to be associated more with differences in sleep characteristics (i.e. sleep problems and duration), than with morningness-eveningness per se, while the opposite is generally true for alcohol consumption. Lifestyle and personality factors likely also play a critical role. Importantly, our study is the first to identify a subgroup of evening-types who report good sleep characteristics and similar levels of intrapersonal adjustment and academic achievement to that of the majority of morning-types.
