Teun Remmers

52 | Chapter 4 Medical Center approved the study protocol (reference number MEC-2007-163). All parents provided written informed consent. This study used a longitudinal design to evaluate determinants of OP development over time. We limited our sample to participants that were allocated to youth healthcare teams participating in the control condition. In the control condition, all parents (N = 3,942) were requested to fill in and return a baseline questionnaire at enrollment (child age five), which assessed socio-demographic characteristics, family environment and parent-perceived PE and the duration of OP (2007–2010). Specific variables of family environment were based on established theories, such as social cognitive theory (e.g. self- efficacy) (15), theory of planned behavior (e.g. intention, attitudes) (16), and social leaning theory (e.g. modeling of spouses and parents) (17). Variables of perceived PE were based on promising results of earlier studies evaluating the influence of the environment on children’s health behavior (e.g. presence of sidewalks, parent perceived safety) (18). At age seven, duration of OP was assessed again by questionnaire. Records with missing data on the outcomes of interest (i.e. OP at age five and seven, n = 1,895) were excluded from the analyses. By doing so, the population for analysis consisted of N = 2,007 parents and children. Measurements Socio-demographic characteristics The child’s gender, age (in years) and ethnic background were assessed. Child’s ethnic background was considered to be “non-Dutch” when at least one of the parents was born abroad, as defined by Statistics Netherlands. Height and weight of the child were measured at age five by healthcare professionals using standardized protocols (19).Respondents were either the father or the mother of the child, and parental gender was entered as a potential confounder in subsequent analyses. From this point onwards, respondent will be described as “parent.” Parental age and parental education (low, mid- low, mid-high, high) were assessed in the baseline questionnaire (20). Family environment and physical environment A full description of constructs, construct properties, items and response scales is presented in Appendix 1. Child outside play OP was defined by the total duration of unstructured OP of the child in an average week. Note that this is without organized sports, school PE and/or active transport. At both baseline (child age five) and two-year follow-up (child age seven), OP was assessed using an identical set of questions. Total duration of OP was therefore computed in a similar way for both time points, as presented below.