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Factors associated with participation over time in the Avon Longitudinal Study of Parents and Children: a study using linked education and primary care data
John Macleod
Kate Tilling
Rosie P Cornish
Andy Boyd
Novel Coronavirus
Acceso Abierto
Background Dropout from studies can lead to biased exposure-outcome estimates if the outcome is associated with continued participation, but this cannot be investigated using incomplete data. Linkage to external datasets provides a means of obtaining outcome - or proxy outcome - data on non-responders. Methods We examined the association between baseline socio-demographic factors and participation in the Avon Longitudinal Study of Parents and Children. We investigated whether child and adolescent outcomes measured in linked education and primary care data were associated with participation after accounting for baseline factors. To demonstrate the potential for bias, we examined whether the association between maternal smoking and these outcomes differed in the subsample who completed the 19-year questionnaire. Results Lower levels of school attainment, lower GP consultation and prescription rates, higher BMI, special educational needs (SEN) status, not having an asthma diagnosis, depression and being a smoker were all associated with lower participation after adjustment for baseline factors. For example, adjusted odds ratio (OR) for participation comparing ever smokers (by 18 years) to non-smokers: 0.65, 95% CI (0.56, 0.75). The association of maternal smoking differed between the subsample of participants at 19 years and the entire sample, although differences were small and confidence intervals overlapped. For example: for SEN status OR=1.19 (1.06, 1.33) (all participants); OR=1.03 (0.79, 1.45) (subsample). Conclusions Linkage to routine data provides a unique opportunity to compare continuing participators to those who drop out, and the impact this self-selection can have on results. Cohort studies should use linkage to routine data to explore participation and conduct sensitivity analyses. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by the Medical Research Council [MR/L012081] and the Wellcome Trust [WT086118/Z/08/Z]. The UK Medical Research Council (MRC), the Wellcome Trust and the University of Bristol currently provide core funding for ALSPAC [102215/2/13/2]. Data collection is funded from a wide range of sources. This publication is the work of the authors and Rosie Cornish will serve as guarantor for the contents of this paper. RC and KT work in the MRC Integrative Epidemiology Unit funded by the UK Medical Research Council (MC_UU_00011/3) and the University of Bristol. ### Author Declarations All relevant ethical guidelines have been followed; any necessary IRB and/or ethics committee approvals have been obtained and details of the IRB/oversight body are included in the manuscript. Yes All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The authors do not have the authority to share the data that support the findings of this study, due to ALSPAC data access permissions, but any researcher can apply to use ALSPAC data, including the variables used in this investigation. Information about access to ALSPAC data is given on their website: (
Cold Spring Harbor Laboratory Press
Appears in Collections:Artículos científicos

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