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Active (Opt-In) consent underestimates mean BMI-z and the prevalence of overweight and obesity compared to passive (Opt-Out) consent. Evidence from the Healthy Together Victoria and Childhood Obesity Study

Strugnell, Claudia, Orellana, Liliana, Hayward, Joshua, Millar, Lynne, Swinburn, Boyd and Allender, Steven 2018, Active (Opt-In) consent underestimates mean BMI-z and the prevalence of overweight and obesity compared to passive (Opt-Out) consent. Evidence from the Healthy Together Victoria and Childhood Obesity Study, International journal of research and public health, vol. 15, no. 4, pp. 1-11, doi: 10.3390/ijerph15040747.

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Title Active (Opt-In) consent underestimates mean BMI-z and the prevalence of overweight and obesity compared to passive (Opt-Out) consent. Evidence from the Healthy Together Victoria and Childhood Obesity Study
Author(s) Strugnell, ClaudiaORCID iD for Strugnell, Claudia orcid.org/0000-0001-5912-9720
Orellana, LilianaORCID iD for Orellana, Liliana orcid.org/0000-0003-3736-4337
Hayward, Joshua
Millar, Lynne
Swinburn, Boyd
Allender, StevenORCID iD for Allender, Steven orcid.org/0000-0002-4842-3294
Journal name International journal of research and public health
Volume number 15
Issue number 4
Article ID 747
Start page 1
End page 11
Total pages 11
Publisher MDPI
Place of publication BAsel, Switzerland
Publication date 2018-04
ISSN 1660-4601
Keyword(s) BMI
active consent
childhood
non-participation bias
obesity prevalence
passive consent
school
Summary Background: Tracking population trends in childhood obesity and identifying target areas for prevention requires accurate prevalence data. This study quantified the magnitude of non-participation bias for mean Body Mass Index-z scores and overweight/obesity prevalence associated with low (opt-in) compared to high (opt-out) participation consent methodologies.

Methods: Data arose from all Local Government Areas (LGAs) participating in the Healthy Together Victoria Childhood Obesity Study, Australia. Primary schools were randomly selected in 2013 and 2014 and all Grades 4 and 6 students (aged approx. 9-12 years) were invited to participate via opt-in consent (2013) and opt-out consent (2014). For the opt-in wave N = 38 schools (recruitment rate (RR) 24.3%) and N = 856 students participated (RR 36.3%). For the opt-out wave N = 47 schools (RR 32%) and N = 2557 students participated (RR 86.4%).

OUTCOMES: differences between opt-in and opt-out sample estimates (bias) for mean BMI-z, prevalence of overweight/obesity and obesity (alone). Standardized bias (Std bias) estimates defined as bias/standard error are reported for BMI-z.

Results: The results demonstrate strong evidence of non-participation bias for mean BMI-z overall (Std bias = -4.5, p < 0.0001) and for girls (Std bias = -5.4, p < 0.0001), but not for boys (Std bias = -1.1, p = 0.15). The opt-in strategy underestimated the overall population prevalence of overweight/obesity and obesity by -5.4 and -4.5 percentage points respectively (p < 0.001 for both). Significant underestimation was seen in girls, but not for boys.

Conclusions: Opt-in consent underestimated prevalence of childhood obesity, particularly in girls. Prevalence, monitoring and community intervention studies on childhood obesity should move to opt-out consent processes for better scientific outcomes.
Language eng
DOI 10.3390/ijerph15040747
Field of Research 111704 Community Child Health
MD Multidisciplinary
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2018, by the authors
Free to Read? Yes
Use Rights Creative Commons Attribution licence
Persistent URL http://hdl.handle.net/10536/DRO/DU:30108678

Document type: Journal Article
Collections: School of Health and Social Development
Open Access Collection
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Every reasonable effort has been made to ensure that permission has been obtained for items included in DRO. If you believe that your rights have been infringed by this repository, please contact drosupport@deakin.edu.au.