Abstract
ObjectivesThe impact of non-participation due to psychiatric illness on study outcomes in general population studies is insufficiently investigated. Here, we investigate the mental health bias in a population study and the potential impact on estimates of cardiovascular morbidity and overall survival.DesignData were retrieved from nationwide registries.SettingThe Danish General Suburban Population Study (GESUS), a cross-sectional community study conducted in Naestved Municipality, Denmark, from 2010 to 2013.Participants49 707 subjects invited to participate in GESUS.Main outcome measuresFactors related to non-participation were examined using multivariable logistic regression and time-to-event data using Cox proportional hazards models.ResultsOf 21 203 (43%) participants, 823 (3.9%) had a psychiatric diagnosis. Of 28 504 non-participants, 2453 (8.6%) had a psychiatric diagnosis (OR for non-participation 1.84 (95% CI 1.69 to 2.00)). The most under-represented psychiatric disorders in participants were organic mental disorders (5.76 (3.90 to 8.48)), substance abuse (3.12 (2.14 to 4.54)) and schizophrenia (3.12 (2.33 to 4.18)). Overall, more non-participants used psychotropic drugs than participants (1.26 (1.21 to 1.31)), and psychiatric non-participants had higher psychiatric hospital service utilisation than psychiatric participants. Compared with non-psychiatric participants in a 5-year follow-up, psychiatric non-participants had higher rates of cardiovascular events (HR 2.30 (2.07 to 2.56)) and all-cause mortality (3.37 (3.01 to 3.78)) than non-psychiatric non-participants (1.65 (1.48 to 1.83) and 2.26 (2.02 to 2.54), respectively) and psychiatric participants (1.39 (1.21 to 1.59) and 1.23 (1.05 to 1.44), respectively), pinteraction<0.0001 for both outcomes.ConclusionsThis study demonstrates a considerable non-participation bias due to psychiatric illness in a general population health study, potentially leading to distorted estimates of somatic morbidity and mortality. Strategies for better-representing individuals with psychiatric illnesses in population health studies are needed.
Funder
Region Zealand Research Foundation
Naestved Hospital Foundation
The National Board of Health
The Local Government Denmark Foundation
TrygFonden
Johannes Fog's Foundation
Naestved Municipality
Johan and Lise Boserup Foundation
Region Sjælland
Naestved Hospital