Negative emotionality (NE) and positive emotionality (PE) have repeatedly shown to act as vulnerability factors for youth depression. Less research examined the mechanisms through which these reactive temperament traits may differently confer vulnerability to depression. Based on recent integrated models of depression proposing emotion regulation as a key underlying mechanism, the current study aimed to clarify the general and day-to-day relations among temperament, emotion regulation strategies, and depressive symptoms in Dutch-speaking youth (35% boys; M_age = 13.27 years, SD = 1.98) using a cross-sectional (n = 495) and a 7-day daily diary design (n = 469). Self-reported temperament, trait rumination, trait positive refocusing, and depressive symptoms were measured at baseline. State rumination, state positive refocusing, and depressive symptoms were further assessed daily. Whereas results revealed that NE and PE interacted in predicting baseline and daily depressive symptoms, the cross-sectional analyses provide preliminary evidence for the hypothesis that NE and PE each provide unique pathways for understanding vulnerability to depression. Additional analyses in the daily diary study showed NE to be significantly related to trajectories of state rumination. Results contribute to a more nuanced understanding of the associations between temperament, emotion regulation strategies, and depressive symptoms in youth. 

The current study is part of larger research project on emotional wellbeing in youth at the Clinical Developmental Psychopathology Department of Ghent University. The protocol of the study was approved by the Ethical Committee of the Faculty of Psychology and Educational Sciences at Ghent University. Third-year psychology students were instructed to recruit two Dutch-speaking participants between age 10 and 16 of the Belgian–Flemish population with which they were not emotionally involved (no family, friends, etc.) and visit them at home. No other in- or exclusion criteria were put forward. After obtaining both child and parental written informed consent, participants were asked to fill out a paper and pencil test battery comprising measures of overall psychopathology, reactive temperament, and trait ER strategies in a separate room at home. During the assessment, one of the students remained present in the room to answer questions pertaining to the test battery. After completing the home-assessment, participants were asked to participate in the 7-day daily diary study. In the daily diary study, participants were instructed to fill out a shortened test battery on a secure online platform hosted by the Department of Developmental, Personality, and Social Psychology on their own computer at home, starting from the following Monday. The online test battery consisted of three scales assessing (daily) depressive symptoms, state rumination, and state positive refocusing. Participants were told to complete the diary on a daily basis before bedtime. The participants’ parents were given standardized instructions and received a daily reminder by e-mail or by phone at the end of the day during that week. Participation was not remunerated. 

Of all of the participants, 36 youth did not fill out the self-report questionnaires during the home visit. These youths did not significantly differ from the current sample in terms of gender and age (all ps ≥ .789). Furthermore, 62 children did not fill out the daily diary because they found it too time-consuming. These youths did not significantly differ from the remaining sample on gender, age, NE, PE, and depressive symptoms at baseline (all ps ≥ .142). 
Preliminary analyses of the cross-sectional data suggested that the percentage of missing data ranged between 0% and 1.4% per item. Comparison of means and covariances of all variables using Little's MCAR-test produced a normed χ² (χ²/df) of 1.05, p > .30, indicating that the data were likely missing completely at random. Consequently, missing item values were imputed following the expectation maximization (EM) algorithm available in SPSS 23.
It is expected that in daily diary studies there will be missing data over the 7 days, as was the case in the current study. Participation across weekly assessment was acceptable. The average number of weekly assessments completed was 5.81 (SD = 1.85) out of a possible 7. In total, 59.4% (279) of participants completed all seven assessments, 14% (66) completed six assessments, 6.8% (32) completed five assessments, 4% (19) completed four assessments, 5.7% (27) completed three assessments, 4.3% (20) completed two assessments and 5.7 % (27) completed one assessment. In order to retain all available information, a specific time point was dropped from the analyses when one time-point was missing instead of dropping a participant from the entire analyses. Comparison of youth that completed all daily assessments of the diary study and youth who didn’t comply revealed that there were no significant differences between youth regarding gender, age, NE, PE, and depressive symptoms in the cross-sectional study, as well as daily levels of depressive symptoms in the daily diary study (all ps ≥ .253).