Time-sensitive testing pressures and COVID-19 outcomes: are socioeconomic inequalities over the first year of the pandemic explained by selection bias?

Alice R Carter; Gemma L Clayton; M Carolina Borges; Laura D Howe; Rachael A Hughes; George Davey Smith; Deborah A Lawlor; Kate Tilling; Gareth J Griffith

doi:10.1186/s12889-023-16767-5

Time-sensitive testing pressures and COVID-19 outcomes: are socioeconomic inequalities over the first year of the pandemic explained by selection bias?

BMC Public Health. 2023 Sep 26;23(1):1863. doi: 10.1186/s12889-023-16767-5.

Authors

Alice R Carter^{1

2}, Gemma L Clayton^{1

2}, M Carolina Borges^{1

2}, Laura D Howe^{1

2}, Rachael A Hughes^{1

2}, George Davey Smith^{1

2}, Deborah A Lawlor^{1

2}, Kate Tilling^{1

2}, Gareth J Griffith^{3

4}

Affiliations

¹ MRC Integrative Epidemiology Unit, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK.
² Population Health Sciences, Bristol Medical School, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK.
³ MRC Integrative Epidemiology Unit, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. g.griffith@bristol.ac.uk.
⁴ Population Health Sciences, Bristol Medical School, University of Bristol, Oakfield House, Oakfield Grove, Bristol, BS8 2BN, UK. g.griffith@bristol.ac.uk.

Abstract

Background: There are many ways in which selection bias might impact COVID-19 research. Here we focus on selection for receiving a polymerase-chain-reaction (PCR) SARS-CoV-2 test and how known changes to selection pressures over time may bias research into COVID-19 infection.

Methods: Using UK Biobank (N = 420,231; 55% female; mean age = 66.8 [SD = 8·11]) we estimate the association between socio-economic position (SEP) and (i) being tested for SARS-CoV-2 infection versus not being tested (ii) testing positive for SARS-CoV-2 infection versus testing negative and (iii) testing negative for SARS-CoV-2 infection versus not being tested. We construct four distinct time-periods between March 2020 and March 2021, representing distinct periods of testing pressures and lockdown restrictions and specify both time-stratified and combined models for each outcome. We explore potential selection bias by examining associations with positive and negative control exposures.

Results: The association between more disadvantaged SEP and receiving a SARS-CoV-2 test attenuated over time. Compared to individuals with a degree, individuals whose highest educational qualification was a GCSE or equivalent had an OR of 1·27 (95% CI: 1·18 to 1·37) in March-May 2020 and 1·13 (95% CI: 1.·10 to 1·16) in January-March 2021. The magnitude of the association between educational attainment and testing positive for SARS-CoV-2 infection increased over the same period. For the equivalent comparison, the OR for testing positive increased from 1·25 (95% CI: 1·04 to 1·47), to 1·69 (95% CI: 1·55 to 1·83). We found little evidence of an association between control exposures, and any considered outcome.

Conclusions: The association between SEP and SARS-CoV-2 testing changed over time, highlighting the potential of time-specific selection pressures to bias analyses of COVID-19. Positive and negative control analyses suggest that changes in the association between SEP and SARS-CoV-2 infection over time likely reflect true increases in socioeconomic inequalities.

Keywords: COVID-19; Health inequalities; Linkage studies; Selection bias; Socioeconomic position.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aged
COVID-19 Testing
COVID-19* / diagnosis
COVID-19* / epidemiology
Communicable Disease Control
Educational Status
Female
Humans
Male
Pandemics
SARS-CoV-2
Selection Bias

Abstract

Publication types

MeSH terms

Grants and funding