1 INTRODUCTION

The ‘first wave’ of the COVID-19 pandemic in the UK was abating by the summer of 2020 (Kontis et al., 2020), and citizens were experiencing respite from the government-imposed restrictions on social, economic, and educational related activities that had been in place since March 2020 to control the spread of the virus. For example, in August 2020, ‘shielding’ initiatives requiring ∼2 million elderly and/or medically vulnerable individuals to self-isolate to avoid contracting COVID-19 were paused across most of the UK (UK Government, 2020a). A month-long ‘Eat Out to Help Out’ scheme offering discounted meals at indoor venues was launched to support the reopening of businesses (UK Government, 2020c). Employers were actively encouraged to reassure employees that it was safe to return to office workplaces (UK Government, 2020e). Also, the majority of primary and secondary schools re-opened for face-to-face teaching for all students (UK Government, 2020b).

During this time, concerns were raised by public health experts about the potential impact of an equally, if not more, devastating ‘second wave’, evidence of which was already being reported in parts of Europe, which was predicted to hit the UK by autumn 2020 (Academy of Medical Sciences, 2020; Looi, 2020; Mahase, 2020; Middleton et al., 2020). By October 2020, as the UK COVID-19 reproduction rate was estimated to be between 1.3 and 1.5, signalling high levels of infection transmissibility in communities, one-quarter of the UK population (∼16.8 million citizens) was forced back into lockdown (UK Government, 2020d). The Office for National Statistics (2020) reported that COVID-19 cases were increasing rapidly, and that COVID-19 related hospital admissions were close to the peak of the ‘first wave’ in spring 2020 (see Figure 1). On 5 November 2020, the UK Prime Minister announced a second national lockdown for England, initially for 4 weeks (UK Government, 2020g), and the government ‘furlough scheme’, which provides up to 80% income support for unemployed workers, was extended until March 2021 (UK Government, 2020f). On 2 December 2020, the lockdown was replaced with a revised regional COVID-19 tier-system, which re-imposed regulations on social gatherings (UK Government, 2020h). On this same date, the UK became the first country in the world to approve the Pfizer-BioNTech vaccine (Ledford et al., 2020) and the vaccination rollout commenced 6 days later. The Oxford-AstraZeneca vaccine was anticipated to be approved and subsequently deployed in January 2021 (UK Government Coronavirus (COVID-19) in the UK, 2021).

Graphical presentation of the number of daily COVID-19 cases and deaths in the UK, sourced from Our World in Data, 2020, aligned to the COVID-19 Psychological Research Consortium (C19PRC) Study survey waves. Note: New daily deaths and cases depicted as 7-day rolling average

In late 2020, whilst grappling with preparations for an upcoming COVID-19 surge, as well as planning the population-wide COVID-19 vaccination rollout, the UK government was facing a major historical political event: the end of the Brexit transition period on 31 December 2020 (Wright & Etherington, 2020). The crippling economic impacts of the protracted pandemic, compounded by uncertainty surrounding the short-to-medium term impacts of Brexit, was predicted to widen existing regional inequalities in the UK (Bhattacharjee et al., 2020; Petrie & Norman, 2020). The decision to hold the 2016 European Union referendum, and the voting outcome of that referendum, had already resulted in societal division across the UK and Europe (Hobolt, 2018; Outhwaite, 2017), particularly in relation to views on culture, migration, racism, national identity, and political ideologies (Bachmann & Sidaway, 2016; Corbett, 2016). Moreover, the pandemic itself, coupled with states' initiatives to control the spread of the disease across populations, may have contributed substantially to the rise of nationalism and its social relevance on a global scale (Bieber, 2020; Woods et al., 2020).

It is against this backdrop that the fourth wave of the C19PRC Study (hereafter referred to as C19PRC-UKW4) was conducted in the UK during November–December 2020. Established in March 2020, the C19PRC Study is a dynamic, online, longitudinal, multi-country study which aims to evaluate the psychological, socio-economic, and political impacts of the pandemic on the lives of adults living in the UK, Republic of Ireland, Spain, and Italy (McBride et al., 2020). The UK-strand of the C19PRC Study (C19PRC-UK) is the ‘parent’ strand of the Consortium upon which other countries model their survey design, content, and fieldwork procedures. Methodological reports for the C19PRC Study in the UK (Wave 1, March 2020; Wave 2, April 2020; Wave 3, July/August 2020) and other countries are available elsewhere (Bruno et al., 2021; Hyland, Vallières, Shevlin, et al., 2021; McBride et al., 2020, 2021; Valiente et al., 2020, 2021).

1.1 Brief overview of C19PRC Study methodological framework for the C19PRC-UKW4

Collecting data on adults' mental health difficulties (e.g. anxiety, depression, and traumatic stress) at each survey wave, using standardised and validated measures, is a fundamental design feature of the C19PRC Study. Our study has spearheaded COVID-19-related mental health research through the production of timely, high-quality research articles, the findings of which have already demonstrated relatively stable prevalence estimates for depression, anxiety, and COVID-19 traumatic stress during the first 6 months of the pandemic in the UK and Ireland (Hyland, Vallières, Daly, et al., 2021; Shevlin et al., 2021).

The C19PRC Study was designed to go beyond the collection of self-reported survey data at each wave. For example, in this fourth wave, a ‘survey list experiment’ was conducted to assess respondents' compliance with government-imposed public health regulations (for details, see Supporting Information S2: Section 2.2.12.2).

Considerable efforts have been made to maximise participant retention at each wave post-baseline to minimise bias in survey estimates, and this strategy has been successful to date (i.e. ∼60% retention of participants over three waves) (McBride et al., 2021). Moreover, new participants were recruited into the cohort at Wave 3 (C19PRC-UKW3) so that the cross-sectional sample at each wave would continue to be (1) representative of the UK adult population (i.e. new participants were recruited to ‘top-up’ baseline quotas, determined by age, gender, and household income, due to modest levels of attrition) and (2) large enough (n > 2K adults) to conduct sub-group analyses for core study outcomes.

This paper describes the fieldwork procedures for C19PRC-UKW4. Two key decisions were made during the planning phase: (1) to prioritise collection of data on respondents' socio-political views, attitudes, and behaviours to assess the combined impact of Brexit and the COVID-19 pandemic on adults' national identity, and how this might in turn shape their responses to, and experiences of, the pandemic; and (2) to recruit new respondents into the study by oversampling adults from the devolved UK nations (Wales, Scotland, and Northern Ireland), which would facilitate robust between-country comparisons for a range of important socio-political outcomes, in addition to the core mental health outcomes. Here, we (i) examine patterns of attrition in the C19PRC Study by this fourth wave and whether these could be predicted by baseline mental-health attributes, psychological characteristics, as well as socio-demographic factors; (ii) conduct and assess weighting procedures to manage attrition in the longitudinal panel; (iii) determine the success of sample replenishment and oversampling procedures conducted at C19PRC-UKW4; and (iv) describe the prevalence of common mental disorders among participants in the C19PRC-UKW4 sample, as well as their socio-demographic characteristics and political-related beliefs and behaviours.

2 METHOD 2.1 C19PRC-UKW4: fieldwork procedures 2.1.1 Fieldwork organisation overview

The survey company Qualtrics conducted the fieldwork for C19PRC-UKW4. Qualtrics partners with over 20 online sample providers to supply a network of diverse, quality respondents to their worldwide client base and, to date, has completed more than 15,000 projects across 2500 universities worldwide.

2.1.2 Procedure

C19PRC-UKW4 commenced on 25 November 2020, approximately 4 months after the completion of C19PRC-UKW3 (conducted during July–August 2020). C19PRC-UKW4 comprised two phases.

Phase 1 comprised two strands. Qualtrics re-contacted all adults who participated in any previous wave(s) (N = 2878) via email, SMS, or in-app notifications and invited them to participate further in this survey (invitations were tailored to remind adults of their participation in previous survey waves). Only 2025 of these eligible respondents participated at baseline and were being invited to participate in a fourth survey; the remaining 853 first entered the panel at C19PRC-UKW3 and were being invited to participate in their first follow-up survey. Phase 1 fieldwork was completed on 22 December 2020.

Fieldwork for Phase 2 (sample replenishment and oversampling) was conducted between 25 November and 19 December 2020. Similar to the process of recruitment at baseline, new participants for Phase 2 were sampled from Qualtrics' partners' existing survey panels and were alerted to the C19PRC-UKW4 by Qualtrics in one of two ways: (1) they opted to enter studies they were eligible for by signing up to a panel platform; or (2) they received automatic notification through a partner router which alerted/directed them to studies for which they were eligible. To avoid self-selection bias, survey invitations provided only general information and did not include specific details about the contents of the survey. Participants were required to be adults, able to read and write in English, and resident in the UK. No other exclusion criteria were applied. All panel members routinely received an incentive for survey participation (e.g. gift cards), based on the length of the survey, their specific panellist profile, and target acquisition difficulty, amongst other factors. Qualtrics' partners released invitations in batches and, after the initial invitation was received, respondents who had not completed the survey were sent two reminders to encourage them to participate. The first reminder was sent approximately 36–48 h after the initial survey invite, with the second reminder sent another 36–48 h after this first reminder.

2.1.3 Informed consent process

Participants were informed about the purpose of the C19PRC Study, that their data would be treated in confidence, that geolocating would be used to determine the area in which they lived (in conjunction with their residential postcode stem), and of their right to terminate participation at any time. Participants were also informed that some topics might be sensitive or distressing. Information about how their data would be stored and analysed by the research team was also provided. Participants were also informed that they would be re-contacted at a later date to invite them to participate in subsequent survey waves. Participants provided informed electronic consent prior to completing the survey and were directed to contact the NHS website upon completion if they had any concerns about COVID-19.

2.1.4 Compliance with General Data Protection Regulation (GDPR)

C19PRC data will be stored confidentially in line with GDPR. When the study data is deposited with the UK Data Service, location data will be removed and replaced with relevant socioeconomic summary data (e.g. area-level deprivation and population density data). All other personal data will also be removed.

2.1.5 Quality control

Qualtrics are committed to delivering high-quality survey data from online survey panels and multiple validation checks are conducted on the C19PRC-UK data to ensure this target is met. First, the survey is piloted (‘soft launch’; n = 100) prior to the fieldwork going live (‘full launch’) to rectify sequencing/coding errors and omissions prior to the full launch. The soft launch also calculate the median survey completion time, which provides an opportunity to tailor the content to ensure the median survey time does not exceed 30 min; this is important to minimise respondent burden and maximise participation over time. For C19PRC-UKW4, a soft launch was conducted (comprising ∼50 respondents) for each phase. The median survey completion times were 23 min 17 s for Phase 1 and 23 min 7 s for Phase 2. These respondents were excluded from the final sample for that Phase. Given the median times were under the 30-min threshold, additional measures were included in the survey prior to the full launch. Second, each participant must achieve ‘legitimate respondent status’ upon entry into the survey. This means that the respondent must spend a minimum amount of time completing the survey (i.e. half the median soft launch completion time for that wave) the first time they participate. Respondents who do not achieve this status are flagged as ‘speeders’ and removed from the study. And third, any respondent who does not meet the inclusion criteria, or who does not complete the survey in full, is removed from the final sample for that Phase.

2.2 Measures

Table 1 provides an overview of the C19PRC-UKW4 survey content by Phase (see Supporting Information S2 for details of all measures administered).

TABLE 1. Overview of content of C19PRC Study Wave 4 (Phases 1 and 2), United Kingdom (UK), November – December, 2020 Theme Content C19PRC Wave 4 Phase 1 Phase 2 Demographics Age, gender, ethnicity, marital status, economic activity, country of residence, country of birth, born in the UK, key/essential worker status, urbanicitya, level of education†, religion†, self-reported social class, perceived social rank X X†only Housing characteristics Living alone X X Number of adults living in household X X Parental and children in the home status X X Housing tenurea X X Residential details (type of property; number of bedrooms; length at property)a X X Household finances Estimated annual gross household income X X Change in monthly household income during pandemic X X Use of savings/increasing debt during pandemic X X Made saving due to pandemic X X Concern over household finances being negatively affected due to pandemic X X Perceived future financial security X X Receiving benefits X X Difficulty paying bills X X Food insecurity: pre-pandemic and currently X X Working hours Number of hours worked weekly pre/post pandemic X X Number of hours would like to be working X X Health conditions Existence of any major underlying health conditions – self X Existence of any major underlying health conditions – immediate family member X Currently pregnant – self (partner) X X Number of weeks pregnant, if applicable X X Currently pregnant – immediate family member X X Self-rated health X X COVID-19 Sourcing of information (newspapers, TV, radio, social media, internet, etc.) X Level of trust in information source X Anxiety-level relating to COVID-19 X X Confidence in response to COVID-19 pandemic X X Perceived threat of COVID-19 X X Perceived individual risk contracting COVID-19 over next 6 months X X Perceived severity of COVID-19 symptoms if infected/reinfected X X Experiences of self-isolation X X Experiences of children in the home self-isolating X X Experience of being infected with COVID-19 (self and family member/friend) X X Experience of being tested for COVID-19 (symptoms/location of testing/diagnosis) X Knowing someone close (family member/friend) who has tested positive for COVID-19 X X Knowing someone close (family member/friend) who has tested died due to COVID-19 X X Behaviour – engagement with social distancing X X COVID-19 vaccine acceptability (self) X X COVID-19 vaccine acceptability (child) X X Beliefs about vaccines made available to the public X X Support/opposition for mandatory vaccination X X Predicted course of the pandemic X X Support/opposition for restrictions in case of second wave X X Perceived compliance with lockdown rule by different demographic groups (e.g. students, migrants, etc.) and nationally X X Understanding of COVID-19 restrictions and regulations X X Perceived importance of factors affecting lockdown decisions X X Survey list experiment relating to social distancing/adherence to lockdown rules X X Mental Health Depression: Patient Health Questionnaire-9 (Kroenke et al., 2001) X X Anxiety: Generalised Anxiety Disorder Scale-7 (Spitzer et al., 2006) X X Traumatic Stress International Trauma Questionnaire (Cloitre et al., 2018) X X Paranoia: Persecution and Deservedness Scale (Melo et al., 2009) X X Self-harm, suicidal thoughts and suicide attempts X X Treatment for mental health difficulties X X Psychological factors Personality: Big-Five Inventory-10 (Rammstedt & John, 2007) X X Loneliness: Loneliness Scale (Hughes et al., 2004) X X Religiosity: Monotheist and Atheist Beliefs Scale (Alsuhibani et al., 2021) X X Empathy: Interpersonal Reactivity Index (Davis, 1980) X Conspiracy theories: Conspiracy Mentality Scale (Imhoff & Bruder, 2014) X X Hopefulness: Brief-H-Positive (Fraser et al., 2014) X X Happiness: degree of happiness yesterday X X Life satisfaction X X Aspects of life better/worse since pandemic X X Wellbeing: Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS, short 7-item version) (Stewart-Brown et al., 2009) X X Cognitive reflection task X Social engagement with family and friends (Seeman et al., 2011) X Socio-political views/related behaviours Voting behaviour last general Election X Voting behaviour European Referendum X Measure of ‘left-wing’ or ‘right-wing’ on social and economic issues X Satisfaction with how government/institutions handling pandemic X X Patriotism/nationalism X X Social dominance: Social Dominance Scale (Ho et al., 2015) X X Authoritarianism: Very Short Authoritarianism Scale (Bizumic & Duckitt, 2018) X X Attitudes towards migrants X X Political party identification X Citizenship X X National identity (degree of British & Irish identity, importance of identity, pride in identity) X X National belonginess X X Positive/Negative feelings towards flags (British, English, Welsh, Scottish, Irish, EU) X X Positive/Negative feelings towards people of UK and Ireland X X Place resentment X X Attitudes towards an Irish border poll (support and predicted voting) X X Support for an all-Ireland COVID-19 strategy X X Attitudes towards a Scottish Independence Referendum (support and predicted voting) X X English identity (Northerner/Southerner) X X North/South England resentment X X UK remaining united – perceived likelihood and preference X X Languages (Scots, Ulster Scots, Scot Gaelic, Welsh & Irish) X X Hindsight attitudes towards Brexit X X Perceived impact of Brexit on UK X X Brexit predictions X X EU Referendum voter identification X X Populism X X Trust Institutions X X Purchasing behaviours Increased purchasing for specific items (e.g. dried food) during pandemic X X Perceptions of supermarket stock levels X X Purchasing of specific food types (e.g. healthy, convenient, etc.) X X Seasonal items Food and present affordability at Christmas X X Food and present availability at Christmas X X Worry about visiting family/friends over Christmas X X Perceived difficulty visiting family/friends over Christmas X X Note: Refer to Supporting Information S2 for detailed information on all study measures. a These items only asked at Phase 1 if respondent reported that they had moved home since last completing the survey. † Level of education and religion were only measured at Phase 2 only. 2.2.1 Study variables

These baseline (C19PRC-UKW1) variables were used for attrition analyses for C19PRC-UKW4: gender (females vs. males); age (18–24 years olds vs. 25–34 years, 35–44 years, 45–54 years, 55–64 years, and 65+ years groups); household income (≤£15,490 per annum vs. £15,491–£25,340, £25,341–£38,740, £38,741–£57,903, and ≥£57,931 bands); economic activity (employed vs. other); ethnicity (White vs. other); born in UK (yes vs. no); urbanicity (living in city vs. suburb, town or rural location); education (post-secondary education vs. other); religion (atheist or agnostic vs. any religion); household composition (living alone vs. other; children <18 years living in household vs. other); physical health (self-reported chronic health condition vs. other); probable depression diagnosis (score of ≥10 on the Patient Health Questionnaire-9 vs. other); probable generalised anxiety diagnosis (score of ≥10 on the Generalised Anxiety Disorder-7 vs. other); probable PTSD diagnosis (using the International Trauma Questionnaire's diagnostic algorithm for PTSD caseness relating to experience of COVID-19 vs. other); mental health treatment (current or past treatment for mental health problems vs. other); loneliness (score of ≥6 on the Loneliness Scale); neuroticism (total score on the neuroticism subscale of the Big-Five Inventory-10); somatisation (total score on the Patient Health Questionnaire-15); resilience (total score on the Brief Resilience Scale); paranoia (total score on the Persecution and Deservedness Scale); death anxiety (total score on the Death Anxiety Inventory); intolerance of uncertainty (total score on the Intolerance of Uncertainty Scale); and COVID-19 anxiety (total score on single item indicator).

In addition, these variables (same categorisation as above) were used to describe the C19PRC-UKW4 sample characteristics and for attrition analyses for C19PRC-UKW4: gender; age; household income; ethnicity; economic activity; birthplace; household composition; urbanicity; depression; anxiety; PTSD; physical health condition; and voting opinions and behaviours (i.e. 2016 EU Referendum; Brexit hindsight; UK General Election 2019 vote; and political party affiliation).

2.3 Ethical approval

Ethical approval for the project was provided by the University of Sheffield (Reference number 033759).

2.4 Data analysis plan and weighting procedures

Four sets of analyses are presented. First, the longitudinal panels starting at (i) baseline, and (ii) the previous wave (C19PRC-UKW3), were considered separately, and overall, for the purposes of calculating re-contact rates and conducting attrition analyses. Specifically, a multinomial logistic regression tested the associations between a range of baseline socio-demographic, mental health conditions, and psychological factors and levels of participation across the four waves of the C19PRC Study (i.e. comparing completion of the baseline survey only to completion in any 2, 3 or all four subsequent waves). For all adults eligible for follow-up at C19PRC-UKW4, responders and non-responders at were compared on a range of socio-demographic characteristics, using chi-square tests.

Second, post-stratification survey weighting was conducted using a technique known as survey raking or sample-balancing, using the ‘anesrake’ package in R (Pasek & Pasek, 2018). Raking is one common method of adjusting survey data to ensure that the distribution of the characteristics of a given sample closely mirror the known population distribution. In practice, this means the C19PRC-UKW1 sampling quotas for age, gender, and household income, as well as the baseline proportions achieved for ethnicity, urbanicity, household composition, and being born or raised in the UK, were imposed on the sample of responders obtained at Phase 1, and the raking algorithm was conducted to produce, and iteratively adjust, a weight value for each case in the sample until the sample distribution aligned with the population distribution for the chosen characteristics (DeBell & Krosnick, 2009).

Third, the outcome of recruitment at Phase 2 for the replenishment or ‘top-up’ strand was assessed by comparing the characteristics of adults in the combined Phase 1 and Phase 2 samples (excluding the oversample) with respect to gender, age, and household income, compared to the target sampling quotas specified at baseline to obtain a nationally representative sample of UK adults. The percentage differences between the baseline and C19PRC-UKW4 quota bands for gender, age, and household income were calculated.

And fourth, the socio-demographic, mental health, and political characteristics of the C19PRC-UKW4 sample were assessed using counts and frequencies (weighted, where appropriate) and comparisons across the sample strands using chi-square tests.

3 RESULTS

Figure 2 illustrates the outcome of recruitment of C19PRC-UKW4, Phase 1 and Phase 2.