Mean BMI-for-age Z-score values in children aged 6–9 years by monthly period in three countries in COSI round 1. ANOVA: analysis of variance; BMI: body mass index; BMI/A: BMI-for-age; COSI: Childhood Obesity Surveillance Initiative; WHO: World Health Organization. Notes. Body weight was adjusted for the clothes worn: country-specific clothes adjustment weights by Sweden; average non-country-specific adjustment weights by Belgium and the Czech Republic. Only children whose age fell within the country-specific targeted age group(s) (see Table 1) and those with a BMI/A Z-score value between –5 and +5 relative to the WHO growth reference median [13] were included. By targeted age group, monthly BMI/A Z-score values were computed for the months that included at least 5% of the total group of children in a country-specific dataset. °Statistically significant difference of mean value across monthly periods for the indicated age group (two-way ANOVA without interaction term; ).