Teun Remmers

54 | Chapter 4 Drop-out analyses were performed by means of t-tests for continuous socio-demographic variables (child age, child BMI and parental BMI) and chi-square tests for categorical variables (child gender, child ethnic background, parental ethnic background and parental educational level). All analyses were performed with SPSS version 20.0 (IBM Corp., NY, USA). Multi-collinearity seemed to be a minor issue, as all individual predictors showed variance inflation factors of < 10 (22). Results Baseline characteristics Table 1 shows the characteristics of the study population at baseline. Of the children, 50.5% were boys and 49.5% were girls. Children were predominantly of Dutch ethnic background (91.1%). Boys were older than girls and engaged in more minutes of OP than girls. In total, 76.3% of the children engaged in 60 or more minutes of OP per day (i.e. met the WHO guideline of PA). Respondents were predominantly mothers (91.0%), and 95.2% were of Dutch ethnic background. Regarding family environment of the participating children, only 11.3% perceived improving their OP as difficult. Regarding perceived PE, parents of boys perceived more safety in the evening compared to parents of girls. Compared to children with missing data, the population for analysis consisted of a higher percentage of children with a Dutch ethnic background, a higher percentage of parents with a Dutch ethnic background and a higher percentage of high education parents (all p < 0.05). This means that relatively lower educated parents were more likely to have one or more missing values on their OP. Table 1: Baseline characteristics at child age five years Total (n =2007) Boys (n =1013) Girls (n = 994) Child socio-demographics Age at baseline; mean years (sd) (missing n = 6) 5.75 (0.42) 5.77 (0.42) 5.72 (0.41) Ethnic background; n Dutch (%) (missing n = 27) 1804 (91.10) 996 (98.61) 974 (98.38) BMI; mean kg/m2 (sd) (missing n = 6) 15.39 (1.47) 15.42 (1.35) 15.36 (1.59) Average minutes of outside play; mean (sd) (missing n =0) 108.99 (65.01) 112.72 (65.86) 104.72 (63.41) Outside play ≥ 60 minutes per day, n (%) (missing =0) 76.3 78.9 73.6