Non-response and external validity in a school-based quasi-experimental study ‘The Healthy Primary School of the Future’: A cross-sectional assessment

Abstract

Limited evidence is available about (non)-representativeness of participants in health-promoting interventions. The Dutch Healthy Primary School of the Future (HPSF)-study is a school-based study aiming to improve health through altering physical activity and dietary behaviour, that started in 2015 (registered in ClinicalTrials.gov on 14-06-2016, NCT02800616 ). The study has a response rate of 60%. A comprehensive non-responder analysis was carried out, and responders were compared with schoolchildren from the region and the Netherlands using a cross-sectional design. External sources were consulted to collect non-responder, regional, and national data regarding relevant characteristics including sex, demographics, health, and lifestyle. The Chi-square test, Mann-Whitney U test, or Student's t -test were used to analyse differences. The analyses showed that responders ( n = 494) were comparable with non-responders ( n = 348) and regional data ( n = 6172) with regard to sex and health. Responders did not significantly differ from regional data with regard to lifestyle. Responders had significantly higher educated parents compared to non-responders and were more often of autochthonous ethnicity compared to regional data. Major differences were observed between responders and schoolchildren in the Netherlands, regarding, among others sex, ethnicity, and parental employment rates. We conclude that a potential healthy-volunteer effect in the HPSF-sample is limited. External validity is high when compared to the regional population but low when compared to the national sample. For future intervention studies, we advise to evaluate outcome measures according to regional/national standards and to cooperate with external parties in early stages of research to be able to assess and enhance generalisability.

Can the Healthy Primary School of the Future offer perspective in the ongoing obesity epidemic in young children? A Dutch quasi-experimental study

“…However, due to this design, we were able to test the effectiveness in terms of differences in children’s BMI z-scores between the three school groups over time, and were also able to enrol schools on the basis of motivation, which reflects the real-life situation of school health promotion. Moreover, participants did not significantly differ from non-responders in the participating schools and other children in the region with regard to health and lifestyle 44. The lack of randomisation could, however, have resulted in confounding bias.…”

Unravelling the Effects of the Healthy Primary School of the Future: For Whom and Where Is It Effective?

“…It should be noted though that since all the schools are located in a low SES area, the SES tertiles used in this study are relative and not absolute scores. This means that the average SES score of children in this study sample is low compared to the average of the Netherlands [36]. Nevertheless, the differences in effect at home among children with lower and higher socioeconomic background demonstrate the interaction between two main microsystems of a child, i.e., school and home.…”

The Effects of the Healthy Primary School of the Future on Children’s Fruit and Vegetable Preferences, Familiarity and Intake

“…The current study is part of the overall HPSF research project executed by a large multidisciplinary research team. Previous studies reported on the study design [ 31 ], research approach [ 32 ], process evaluation [ 33 ], non-response, and external validity [ 34 ]. Furthermore, various reports of this project revealed positive intervention effects on various health-related outcomes in children (e.g., BMI z-score, waist circumference, PA, and dietary behaviors) [ 35 , 36 , 37 , 38 ].…”