Recruiting and retaining community-based participants in a COVID-19 longitudinal cohort and social networks study: lessons from Victoria, Australia

Abstract

Background Longitudinal studies are critical to informing evolving responses to COVID-19 but can be hampered by attrition bias, which undermines their reliability for guiding policy and practice. We describe recruitment and retention in the Optimise Study, a longitudinal cohort and social networks study that aimed to inform public health and policy responses to COVID-19. Methods Optimise recruited adults residing in Victoria, Australia September 01 2020–September 30 2021. High-frequency follow-up data collection included nominating social networks for study participation and completing a follow-up survey and four follow-up diaries each month, plus additional surveys if they tested positive for COVID-19 or were a close contact. This study compared number recruited to a-priori targets as of September 302,021, retention as of December 31 2021, comparing participants retained and not retained, and follow-up survey and diary completion October 2020–December 2021. Retained participants completed a follow-up survey or diary in each of the final three-months of their follow-up time. Attrition was defined by the number of participants not retained, divided by the number who completed a baseline survey by September 302,021. Survey completion was calculated as the proportion of follow-up surveys or diaries sent to participants that were completed between October 2020–December 2021. Results At September 302,021, 663 participants were recruited and at December 312,021, 563 were retained giving an overall attrition of 15% (n = 100/663). Among the 563 retained, survey completion was 90% (n = 19,354/21,524) for follow-up diaries and 89% (n = 4936/5560) for monthly follow-up surveys. Compared to participants not retained, those retained were older (t-test, p < 0.001), and more likely to be female (χ2, p = 0.001), and tertiary educated (χ2, p = 0.018). Conclusion High levels of study retention and survey completion demonstrate a willingness to participate in a complex, longitudinal cohort study with high participant burden during a global pandemic. We believe comprehensive follow-up strategies, frequent dissemination of study findings to participants, and unique data collection systems have contributed to high levels of study retention.

Cohort profile: Recruitment and retention in a prospective cohort of Canadian health care workers during the Covid-19 pandemic

“…Low attrition rates over multiple contacts are rare in community-based studies, although de Graaf et al [10] achieved a 20% attrition rate in the first follow-up in a prospective psychiatric epidemiological study. Nguyen et al [11] report an attrition rate of 15% in a community-based cohort of COVID-19 with follow-up of 16 months. Both De Graaf and Nguyen attributed their successful retention to the large time-investment to encourage respondents, as was done in the present study.…”

Cohort profile: recruitment and retention in a prospective cohort of Canadian healthcare workers during the COVID-19 pandemic

“…Low attrition rates over multiple contacts are rare in community-based studies, although de Graaf et al 21 achieved a 20% attrition rate in the first follow-up in a prospective psychiatric epidemiological study. Nguyen et al 22 report an attrition rate of 15% in a community-based cohort of COVID-19 with follow-up of 16 months. Both de Graaf and Nguyen attributed their successful retention to the large time-investment to encourage respondents, as was done here.…”

I know what you did last summer: a cross-sectional study of personal COVID-19 risk reduction strategies used by Victorian adults, December 2021–January 2022

“…The Optimise Study (Optimise) was a longitudinal cohort and social networks study (September 2020–August 2022) that aimed to assess the impact of COVID-19 and associated public health restrictions on segments of the community; a detailed description is available elsewhere. 9 , 10 To achieve this aim, we targeted sampling to participants considered at increased risk of (1) contracting COVID-19; (2) developing severe COVID-19; or (3) experiencing unintended consequences of COVID-19 restrictions were intentionally oversampled, and participants were recruited through flyers, social media, industry and community-based groups. Between 11 and 19 February 2022, these key participants were invited to complete a cross-sectional survey on risk reduction strategies utilised between December 2021 and January 2022 (survey in Supplementary Table 1 ).…”