Teun Remmers

78 | Chapter 5 perceived physical environment, and thus moderates its influence on PA and outside play (14, 58). Strengths and weaknesses Strengths of the present study are, first, the consistent approach of investigating the relationship among the perceived physical environment, parenting influences, social capital, and outside play. Second, this study addresses the moderating influences of the parenting influences and social capital, which is relatively new in the field of health behaviors. Third, a longitudinal design was used, providing insight into associates and moderating factors regarding outside play development across a two-year period. This study had some limitations; namely the relatively high educational level in the KOALA Birth Cohort Study (59) may limit generalization of our results with studies that included participants with relatively lower educational levels. Our dropout analyses showed that there was no important selective dropout and that attrition of was not likely to have influenced our results. We used the meteorological seasons (i.e. autumn, winter, spring, and summer) to adjust for seasonality. However, more precise adjustment for weather-related burdens for children to perform outside play or PA (e.g. rainfall, temperature, and sunshine) may be available. As appropriate adjustment for seasonality is essential in studies investing PA (44), future studies are encouraged to examine the relative influence of these weather conditions on PA and outside play and the role of these weather conditions as a confounder. The comparability of the standardized beta coefficients across model variations indicates consistency and statistical rigor of our models. We acknowledge that our effect sizes were relatively small. However, these small standardized effect sizes may be underestimated due to the relatively high error variance in the parent reported variables (main variables, moderators as well as outcomes). In addition, by allowing respondents to indicate the duration of outside play in five response categories, some measurement error is introduced and precision is compromised. These errors may be subsequently magnified by the multiplication effect regarding the assessment of the frequency of outside play. We thus encourage future studies to improve the reliability and precision of these parental reports by external validation with recent technological advances, examining test-retest methodologies or asking both the father and mother to report on their child’s outside play independently. To date, outside play can only be assessed by parent reports, as a distinction between outside play and other types of PA cannot be made by the currently used objective measurements (e.g. accelerometers or heart-rate monitors). However, recent technological advances provide opportunities for combining global positioning system (GPS), Geographic Information Systems (GIS), and accelerometers. One recent study managed to apply these recent methodologies in an objective measurement instrument