Adolescence is a time of increasing vulnerability for poor mental health, including depression. Sleep disturbance is an important risk factor for the development of depression during adolescence. Excessive electronic media use at night is a risk factor for both adolescents' sleep disturbance and depression. To better understand the interplay between sleep, depressive symptoms, and electronic media use at night, this study examined changes in adolescents' electronic media use at night and sleep associated with smartphone ownership. Also examined was whether sleep disturbance mediated the relationship between electronic media use at night and depressive symptoms. 362 adolescents (12-17 year olds, M = 14.8, SD = 1.3; 44.8% female) were included and completed questionnaires assessing sleep disturbance (short sleep duration and sleep difficulties) and depressive symptoms. Further, participants reported on their electronic media use in bed before sleep such as frequency of watching TV or movies, playing video games, talking or text messaging on the mobile phone, and spending time online. Smartphone ownership was related to more electronic media use in bed before sleep, particularly calling/sending messages and spending time online compared to adolescents with a conventional mobile phone. Smartphone ownership was also related to later bedtimes while it was unrelated to sleep disturbance and symptoms of depression. Sleep disturbance partially mediated the relationship between electronic media use in bed before sleep and symptoms of depression. Electronic media use was negatively related with sleep duration and positively with sleep difficulties, which in turn were related to depressive symptoms. Sleep difficulties were the more important mediator than sleep duration. The results of this study suggest that adolescents might benefit from education regarding sleep hygiene and the risks of electronic media use at night.

Psychologists have not determined the defining characteristics of extroversion. In four studies, the authors tested the hypothesis that extraversion facets are linked by reward sensitivity. According to this hypothesis, only facets that reflect reward sensitivity should load on a higher order extraversion factor. This model was tested against a model in which sociability links fee facets. IDS authors also tested the generalizability of the model in a diverse sample of participants from 39 nations, and they tested the model using widely used extraversion scales. Results of all studies indicate that only facets tfiat reflect reward sensitivity load on a higher order extraversion factor and that this factor correlates strongly with pleasant affect. Although sociability is undoubtedly an important part of extraversion, these results suggest that extraverts' sociability may be a by-product of reward sensitivity, rather than the core feature of the trait.Extraversion has a rich history in the field of personality psychology.

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The present article compares dimensional models of affect with each other. The article focuses on the pleasure–arousal model, the energetic and tense arousal model, and a three‐dimensional model with separate pleasure–displeasure, awake–tiredness, and tension–relaxation dimensions. The results show that the three‐dimensional model cannot be reduced to a two‐dimensional model. Problems of the two‐dimensional models' reductionism are discussed. We conclude that a three‐dimensional description of affect is necessary. However, the three‐dimensional model is not sufficient to account for all aspects of the structure of affect. Copyright © 2000 John Wiley & Sons, Ltd.