JMIR Publications

ABSTRACT

Background:

Sequential mixed-mode surveys using both online surveys and telephone interviews are increasingly being used in observational studies and have been shown to have many benefits, however the application of this survey design has not been evaluated in the context of epidemiological case-control studies.

Objective:

In this paper, we discuss the challenges, benefits, and limitations of using a sequential mixed-mode survey design for a case-control study assessing risk factors during the COVID-19 pandemic.

Methods:

Colorado adults testing positive for SARS-CoV-2 were randomly selected and matched to those with a negative SARS-CoV-2 test result from March-April 2021. Participants were first contacted by text message to complete a self-administered online survey asking about community exposures and behaviors. Those who did not respond were contacted for a telephone interview. We evaluated the representativeness of survey participants to sample populations and compared sociodemographic characteristics, participant responses, and time and resource requirements by survey mode using descriptive statistics and logistic regression models.

Results:

Of enrolled case- and control-participants, most were interviewed by telephone (57.4% and 52.8%, respectively), with overall enrollment more than doubling after interviewers called non-responders. Participants identifying as female or white non-Hispanic, residing in urban areas, and not working outside the home were more likely to complete the online survey. Telephone participants were more likely than online participants to be aged 18-39 or ≥60 years and reside in areas with lower levels of education, more linguistic isolation, lower income, and more people of color. While there were statistically significant sociodemographic differences noted between online and telephone case- and control-participants and their respective sample pools, participants were more similar to sample pools when online and telephone responses were combined. Online participants were less likely to report close contact with an individual with COVID-19 (OR 0.70, 95% CI 0.53–0.94), but more likely to report community exposures including visiting a grocery store/retail shop (OR 1.55, 95% CI 1.13–2.12) or restaurant/café/coffee shop (OR 1.52, 95% CI 1.20–1.92), or attending a gathering (OR 1.69, 95% CI 1.34–2.15) or sport/sporting event (OR 1.05, 95% CI 1.05–1.88). The online survey required an average of 0.03 person-hours per enrolled participant and US $920 in resources, whereas the telephone interview required an average of 5.11 person-hours per enrolled participant and US $70,000 in interviewer wages.

Conclusions:

While we still encountered control recruitment challenges noted in other observational studies, the sequential mixed-mode design was an efficient method for recruiting a more representative group of participants for a case-control study with limited impact on data quality and should be considered during public health emergencies when timely and accurate exposure information is needed to inform control measures.