Teun Remmers

Afterschool PA and the built environment using GPS, GIS and accelerometers | 127 approximately 150.000 residents (36). Population density varies between municipality neighbourhoods (1.8 - 59.0 residents per hectare). Average population density of included neighbourhoods was 19.4 residents per hectare (37). For the baseline measurement, we invited 30 primary schools to participate (initial sample ≈ 1000 children), of which 20 schools agreed to participate. Children in the final year of primary school were all invited to participate in a 7-day accelerometry and GPS monitoring protocol. We recruited children by informing teachers and staff, distributing pamphlets at schools, conducting two educational presentations by the research staff at schools, and by distributing letters for parents or guardians. One year later, participating children were approached again at their secondary school for a follow-up measurement using the same protocol. For the current analyses, only baseline measurements were considered. Ethical approval for the PHASE-kids study was obtained from the research ethics committee of the Maastricht University Medical Centre (reference number 12-4-077). Baseline data were collected from April till July 2015, with an average daily temperature of 15.12 degrees Celsius (SD=4.96) and 77% of the days with < 1.0mm of precipitation (based on registries from a local municipality weather station). Sunset times during this time-period in the centre of the Netherlands were between 20:13 and 22:06 hours (data extracted from http://www.timeanddate.com/sun/netherlands) . Accelerometers and GPS loggers were distributed during school hours, where children received verbal and written instruction about how to wear the devices. Both devices were attached to the waist and worn at the right hip with a single elastic belt. We instructed children to wear the belt during waking hours for 7 consecutive days, only to remove the belt during water-related activities (e.g. swimming, showering), and to recharge the GPS logger every day before going to sleep. Children were asked to record the times and reasons why they took off the devices in a diary. After measurement, devices were collected by the research-staff during school hours, while the child and one of their parents received a verbal and written invitation for an electronic questionnaire. Measurements Socio-demographic measures Parents reported children's name, school, date of birth and address, directly after providing informed consent to participate in the study. In addition, we assessed whether children from divorced parents were residing at two locations. Schools provided detailed class timetables for the data-collection period. Directly after measurement, children and parents filled in an electronic questionnaire focusing on aspects such as perceived environment, child's (travel) behaviours and homework.