Establishing the Minimum Media Time Sample Required to Obtain Reliable Estimates of Children's Digital Media Food Marketing Exposures

Background: The ubiquitous nature of food marketing on digital media likely has a profound effect on children's food preferences and intake. Monitoring children's exposure to digital marketing is necessary to raise awareness of the issue, inform policy development, and evaluate policy implementation and effect. Objectives: This study aimed to establish whether smaller time samples (less time and/or fewer days captured) would provide robust estimates of children's usual exposures to food marketing. Methods: Using an existing data set of children's digital marketing exposures, which captured children's total screen use over 3 d, a reliability assessment was performed.Results: A subsample of 30% of children's usual screen time was found to provide reliable estimates of digital food marketing exposure compared with the full sample (intraclass correlation coefficient: 0.885; Cronbach alpha: 0.884). There was no difference in the rates of marketing (exposures/h) between weekdays and weekend days.Conclusions: These findings enable researchers to reduce the time and resource constraints that have previously restricted this type of monitoring research. The reduced media time sample will further lessen participant burden.