How to mitigate selection bias in COVID-19 surveys: evidence from five national cohorts (preprint)

Background: Non-response is a common problem, and even more so during the COVID-19 pandemic where social distancing measures challenged data collections. As non-response is often systematic, meaning that respondents are usually healthier and from a better socioeconomic background, this potentially introduces serious bias in research findings based on COVID-19 survey data. The goal of the current study was to see if we can reduce bias and restore sample representativeness despite systematic non-response in the COVID-19 surveys embedded within five UK cohort studies using the rich data available from previous time points. Methods: A series of three surveys was conducted during the pandemic across five UK cohorts: National Survey of Health and Development (NSHD, born 1946), 1958 National Child Development Study (NCDS), 1970 British Cohort Study (BCS70), Next Steps (born 1989-90) and Millennium Cohort Study (MCS, born 2000-02). We applied non-response weights and utilised multiple imputation, making use of covariates from previous waves which have been commonly identified as predictors of non-response, to attempt to reduce bias and restore sample representativeness. Results: Response rates in the COVID-19 surveys were lower compared to previous cohort waves, especially in the younger cohorts. We identified bias due to systematic non-response in the distributions of variables including parental social class and childhood cognitive ability. In each cohort, respondents of the COVID-19 survey had a higher percentage of parents in the most advantaged social class, and a higher mean of childhood cognitive ability, compared to the original (full) cohort sample. The application of non-response weights and multiple imputation was successful in reducing bias in parental social class and childhood cognitive ability, nearly eliminating it for the former. Conclusions: The current paper demonstrates that it is possible to reduce bias from non-response and to a large degree restore sample representativeness in multiple waves of a COVID-19 survey embedded within long running longitudinal cohort studies through application of non-response weights or multiple imputation. Such embedded COVID-19 surveys therefore have an advantage over cross-sectional COVID-19 surveys, where non-response bias cannot be handled by leveraging previously observed information on non-respondents. Our findings suggest that, if non-response is appropriately handled, analyses based on the COVID-19 surveys within these five cohorts can contribute significantly to COVID-19 research, including studying the medium and long-term effects of the pandemic.

Long COVID and financial outcomes: Evidence from four longitudinal population surveys (preprint)

Background: Long-term sequelae of COVID-19 (long COVID) include muscle weakness, fatigue, breathing difficulties and sleep disturbance over weeks or months. Using UK longitudinal data, we assessed the relationship between long COVID and financial disruption. Methods: We estimated associations between long COVID (derived using self-reported length of COVID-19 symptoms) and measures of financial disruption (subjective financial well-being, new benefit claims, changes in household income) by analysing data from four longitudinal population studies, gathered during the first year of the pandemic. We employed modified Poisson regression in a pooled analysis of the four cohorts adjusting for a range of potential confounders, including pre-pandemic (pre-long COVID) factors. Results: Among 20,112 observations across four population surveys, 13% reported having COVID-19 with symptoms that impeded their ability to function normally - 10.7% had such symptoms for <4 weeks (acute COVID-19), 1.2% had such symptoms for 4-12 weeks (ongoing symptomatic COVID-19) and 0.6% had such symptoms for >12 weeks (post-COVID-19 syndrome). We found that post-COVID-19 syndrome was associated with worse subjective financial well-being (adjusted relative risk ratios (aRRR)=1.57, 95% confidence interval (CI)=1.25, 1.96) and new benefit claims (aRRR=1.79, CI=1.27, 2.53). Associations were broadly similar across sexes and education levels. These results were not meaningfully altered when scaled to represent the population by age. Conclusions: Long COVID was associated with financial disruption in the UK. If our findings reflect causal effects, extending employment protection and financial support to people with long COVID may be warranted.

BMI across adulthood, COVID-19 and long COVID in two British birth cohorts (preprint)

Longer exposure to obesity, and thus a longer period in an inflamed state, may increase susceptibility to infectious diseases and worsen severity. Previous cross-sectional work finds higher BMI is related to worse COVID-19 outcomes, but less is known about associations with BMI across adulthood. To examine this, we used body mass index (BMI) collected through adulthood in the 1958 National Child Development Study (NCDS) and the 1970 British Cohort Study (BCS70). Participants were grouped by the age they were first overweight (> 25kg/m2) and obese (> 30kg/m2). Logistic regression was used to assess associations with COVID-19 (self-reported and serology-confirmed), severity (hospital admission and contact with health services) and long-COVID reported at ages 62 (NCDS) and 50 (BCS70). Longer exposure to obesity was associated with increased odds of adverse COVID-19 outcomes, but results were mixed and often underpowered. Those with early exposure to obesity were over twice as likely in NCDS (odds ratio (OR) 2.15, 95% confidence interval (CI): 1.17 to 4.00) and three times as likely in BCS70 (OR 3.01, 95% CI: 1.74 to 5.22) to have long COVID. In NCDS they were also over four times as likely to be admitted to hospital (OR 4.69, 95% CI: 1.64 to 13.39). Most associations were somewhat explained by contemporaneous BMI or reported health, diabetes or hypertension; however, the association with hospital admission in NCDS remained. An earlier age of obesity onset is related to COVID-19 outcomes in later life, providing evidence on the long-term impact of raised BMI on infectious disease outcomes in midlife.

Home working and its association with social and mental wellbeing at different stages of the COVID-19 pandemic: Evidence from seven UK longitudinal population surveys. (preprint)

Background: Home working rates have increased since the COVID-19 pandemic's onset, but the health implications of this transformation are unclear. We assessed the association between home working and social and mental wellbeing through harmonised analyses of seven UK longitudinal studies. Methods: We estimated associations between home working and measures of psychological distress, low life satisfaction, poor self-rated health, low social contact, and loneliness across three different stages of the COVID-19 pandemic (T1= Apr-Jun 2020 - first lockdown, T2=Jul-Oct 2020 - eased restrictions, T3=Nov 2020-Mar 2021 - second lockdown), in seven population-based cohort studies using modified Poisson regression and meta-analyses to pool results across studies. Findings: Among 34,131 observations spread over three time points, we found higher rates of home working at T1 and T3 compared with T2, reflecting lockdown periods. Home working was not associated with psychological distress at T1 (RR=0.92, 95%CI=0.79-1.08) or T2 (RR=0.99, 95%CI=0.88-1.11), but a detrimental association was found with psychological distress at T3 (RR=1.17, 95%CI=1.05-1.30). Poorer psychological distress associated with home working was observed for those educated to below degree level at T2 and T3. Men working from home reported poorer self-reported health at T2. Interpretation: No clear evidence of an association between home working and mental wellbeing was found, apart from greater risk of psychological distress associated with home working during the second lockdown, but differences across sub-groups may exist. Longer term shifts to home working might not have adverse impacts on population wellbeing in the absence of pandemic restrictions but further monitoring of health inequalities is required.

Mental health outcomes following COVID-19 infection: Evidence from 11 UK longitudinal population studies (preprint)

Background Evidence on associations between COVID-19 illness and mental health is mixed. We examined longitudinal associations between COVID-19 and mental health while considering: 1) pre-pandemic mental health, 2) time since infection; 3) subgroup differences; and 4) confirmation of infection via self-reported test, and serology data. Methods Using data from 11 UK longitudinal studies, involving 54,442 participants, with 2 to 8 repeated measures of mental health and COVID-19 between April 2020 and April 2021, we standardised continuous mental health scales within each study across time. We investigated associations between COVID-19 (self-report, test-confirmed, serology-confirmed) and mental health using multilevel generalised estimating equations. We examined whether associations varied by age, sex, ethnicity, education and pre-pandemic mental health. Effect-sizes were pooled in random-effects meta-analyses. Outcomes Pooled estimates of the standardized difference in outcome between those with and without self-reported COVID-19 suggested associations with subsequent psychological distress (0.10 [95%CI: 0.06; 0.13], I 2 =42.8%), depression (0.08 [0.05; 0.10], I 2 =20.8%), anxiety (0.08 [0.05; 0.10], I 2 =0%), and lower life satisfaction (−0.06 [-0.08; -0.04], I 2 =29.2%). Associations did not vary by time since infection until 3+ months and were present in all age groups, with some evidence of stronger effects in those aged 50+. Self-reported COVID-19, whether suspected or test-confirmed and irrespective of serology status, was associated with poorer mental health. Interpretation Self-reporting COVID-19 was longitudinally associated with deterioration in mental health and life satisfaction. Our findings have important implications for mental health service provision, given the substantial prevalence of COVID-19 in the UK and worldwide. Funding MRC and NIHR

Disruption of long-term psychological distress trajectories during the COVID-19 pandemic: evidence from three British birth cohorts (preprint)

Importance Mental health disorders were among the leading global contributors to years lived with disability prior to the COVID-19 pandemic onset, and growing evidence suggests that population mental health outcomes have worsened since the pandemic started. The extent that these changes have altered common age-related trends in psychological distress, where distress typically rises until mid-life and then falls in both sexes, is unknown. Objective To analyse whether long-term pre-pandemic psychological distress trajectories have altered during the pandemic, and whether these changes have been different across generations and by sex. Design Cross-cohort study with prospective data collection over a 40-year period (earliest time point: 1981; latest time point: February/March 2021). Setting Population-based (adult general population), Great Britain. Participants Members of three nationally representative birth cohorts which comprised all people born in Great Britain in a single week of 1946, 1958, or 1970, and who participated in at least one of the data collection waves conducted after the start of the pandemic (40.6%, 42.8%, 39.4%, respectively). Exposure(s) Time, COVID-19 pandemic. Main Outcome(s) and Measure(s) Psychological distress factor scores, as measured by validated self-reported questionnaires. Results 16,389 participants (2,175 from the 1946 birth cohort, 52.8% women; 7,446 from the 1958 birth cohort, 52.4% women; and 6,768 from the 1970 birth cohort, 56.2% women) participated in the study. By September/October 2020, psychological distress levels had reached or exceeded the levels of the peak in the pre-pandemic life-course trajectories, with larger increases in younger cohorts: Standardised Mean Differences (SMD) and 95% confidence intervals (CIs) of -0.02 [-0.07, 0.04], 0.05 [0.02, 0.07], and 0.09 [0.07, 0.12] for the 1946, 1958, and 1970 birth cohorts, respectively. Increases in distress were larger among women than men, widening the pre-existing inequalities observed in the pre-pandemic peak and in the most recent pre-pandemic assessment. Conclusions and Relevance Pre-existing long-term psychological distress trajectories of adults born between 1946 and 1970 were disrupted during the COVID-19 pandemic, particularly among women, who reached the highest levels ever recorded in up to 40 years of follow-up data. This may impact future trends of morbidity, disability, and mortality due to common mental health problems.

Adult life-course trajectories of psychological distress and economic outcomes in midlife during the COVID-19 pandemic (preprint)

This study used two British birth cohorts to examine whether pre-pandemic trajectories of psychological distress were associated with a greater risk of changes in financial and employment situation during the pandemic, as well as increased need for government support and use of other methods to mitigate their economic situation. We identified 5 differential life-course trajectories of psychological distress from adolescence to midlife and explored their relation to changes in financial and employment circumstances at different stages during the pandemic from May 2020 to March 2021, applying multinomial logistic regression and controlling for numerous early life covariates. In addition, we ran modified Poisson models with robust standard errors to identify whether different trajectories were more likely to have been supported by the benefit system, payment holidays, borrowing and other methods of mitigating the economic shock. We found that despite the UK governments economic response package economic inequalities for pre-pandemic psychological distress trajectories with differential onset, severity and chronicity across the life-course were exacerbated by the COVID-19 economic shock. Furthermore, the subsequent cut in government support, alongside increases in the cost of living may widen economic inequalities for differential pre-pandemic psychological distress trajectories, which in turn may also worsen mental health. This work highlights, different pre-pandemic trajectories of psychological distress were more vulnerable to economic shock.

Pre-pandemic mental health and disruptions to healthcare, economic, and housing outcomes during COVID –19: evidence from 12 UK longitudinal studies (preprint)

Background The COVID-19 pandemic and associated virus suppression measures have disrupted lives and livelihoods and people already experiencing mental ill-health may have been especially vulnerable. Aim To quantify mental health inequalities in disruptions to healthcare, economic activity and housing. Method 59,482 participants in 12 UK longitudinal adult population studies with data collected prior to and during the COVID-19 pandemic. Within each study we estimated the association between psychological distress assessed pre-pandemic and disruptions since the start of the pandemic to three domains: healthcare (medication access, procedures, or appointments); economic activity (employment, income, or working hours); and housing (change of address or household composition). Meta-analyses were used to pool estimates across studies. Results Across the analysed datasets, one to two-thirds of participants experienced at least one disruption, with 2.3-33.2% experiencing disruptions in two or more domains. One standard deviation higher pre-pandemic psychological distress was associated with: (i) increased odds of any healthcare disruptions (OR=1.30; [95% CI:1.20–1.40]) with fully adjusted ORs ranging from 1.24 [1.09–1.41] for disruption to procedures and 1.33 [1.20– 1.49] for disruptions to prescriptions or medication access; (ii) loss of employment (OR=1.13 [1.06–1.21]) and income (OR=1.12 [1.06 –1.19]) and reductions in working hours/furlough (OR=1.05 [1.00–1.09]); (iii) no associations with housing disruptions (OR=1.00 [0.97–1.03]); and (iv) increased likelihood of experiencing a disruption in at least two domains (OR=1.25 [1.18–1.32]) or in one domain (OR=1.11 [1.07–1.16]) relative to no disruption. Conclusion People experiencing psychological distress pre-pandemic have been more likely to experience healthcare and economic disruptions, and clusters of disruptions across multiple domains during the pandemic. Failing to address these disruptions risks further widening the existing inequalities in mental health.

Changes in the behavioural determinants of health during the coronavirus (COVID-19) pandemic: gender, socioeconomic and ethnic inequalities in 5 British cohort studies (preprint)

BackgroundThe coronavirus (COVID-19) pandemic and consequent physical distancing measures are expected to have far-reaching consequences on population health, particularly in already disadvantaged groups. These consequences include changes in health impacting behaviours (such as exercise, sleep, diet and alcohol use) which are arguably important drivers of health inequalities. We sought to add to the rapidly developing empirical evidence base investigating the impacts of the pandemic on such behavioural outcomes. MethodsUsing data from five nationally representative British cohort studies (born 2001, 1990, 1970, 1958, and 1946), we investigated sleep, physical activity (exercise), diet, and alcohol intake (N=14,297). Using measures of each behaviour reported before and during lockdown, we investigated change in each behaviour, and whether such changes differed by age/cohort, gender, ethnicity, and socioeconomic position (SEP; childhood social class, education attainment, and adult reporting of financial difficulties). Binary or ordered logistic regression models were used, adjusting for prior measures of each health behaviour and accounting for study design and non-response weights. Meta-analyses were used to pool cohort-specific estimates and formally test for heterogeneity across cohorts. ResultsChanges in these outcomes occurred in in both directions ie, shifts from the middle part of the distribution to both declines and increases in sleep, exercise, and alcohol use. For all outcomes, older cohorts were less likely to report changes in behaviours compared with younger cohorts. In the youngest cohort (born 2001), the following shifts were more evident: increases in exercise, fruit and vegetable intake, sleep, and less frequent alcohol consumption. After adjustment for prior behaviour levels, during lockdown females were less likely to sleep within the typical range (6-9 hours) yet exercised more frequently; lower SEP was associated with lower odds of sleeping within the typical range (6-9 hours), lower exercise participation, and lower consumption of fruit and vegetables; and ethnic minorities were less likely than White participants to sleep within the typical range (6-9 hours), exercise less frequently, yet reported less frequent alcohol consumption. ConclusionsOur findings highlight the multiple changes to behavioural outcomes that may have occurred due to COVID-19 lockdown, and the differential impacts across generation, gender, SEP and ethnicity. Such changes require further monitoring given their possible implications to population health and the widening of health inequalities.