New research sheds light on how to boost responses to cohort studies
Annual 45 and Up Study Collaborators’ Meeting at Aerial Function Centre 31 October 2014
Professor Adrian Bauman is the lead author of the study
Professor Adrian Bauman is the lead author of the study

New research from the Sax Institute’s 45 and Up Study has shed light on a quandary long faced by researchers who conduct population-based cohort studies – how to ensure a good response rate to large-scale follow up population-based surveys?

For decades, there has been a decline in response rates to epidemiological cohort studies, the study authors said. However, they noted that it was crucial to ensure strong recruitment and follow-up response rates, given that loss of people in cohort studies may influence the findings from this research, and non-responders may show a socioeconomic gradient or higher mortality than participants who usually complete follow-up questionnaires.

They tested strategies to boost the response rate to a survey, using a sample of participants from the 45 and Up Study, a major longitudinal study into healthy ageing including more than 260,000 adults in NSW.

How to enhance the response rate?

A pilot phase involved a survey for a sub-study known as the SEEF (Social, Economic and Environmental) Study being mailed to 5000 Study participants. The 30-day response rate to the survey was 41.7%.

The researchers then tested three strategies:

  • 1000 participants received an advance notice postcard, followed by a questionnaire two weeks later
  • 1000 participant received the questionnaire, then a reminder letter two weeks later if they failed to return the questionnaire
  • The third group of 1000 participants received both the above strategies

Overall, the three strategies produced a response rate of 53.7% ‒  significantly higher than in the pilot study.

Sending both an advance notice postcard and a reminder questionnaire produced the best response rate (56.4%), followed by sending the reminder (54.1%), then the pre-questionnaire postcard (50.5%), according to the findings published in the journal Emerging Themes in Epidemiology.

For recruitment  among the remaining 92,000 Study participants eligible for the SEEF project, the strategy was adapted to mailing out the initial questionnaire, followed by a reminder letter to non-responders after three weeks, and a second reminder letter with the questionnaire after another three weeks.

The response rate increased further to 61.6% ‒ described by the authors as a reasonable return rate at an acceptable cost, especially when combined with follow up through data linkage.

Lessons for cohort studies

The findings indicated that increasing the follow-up intensity was a successful way of improving response rates, the authors said. This is especially challenging in large-scale studies, where home visits and phone reminders are largely impractical.

“This study has made an important contribution to maximising the follow-up response rate, and consequently the usefulness of the SEEF Study follow up among older Australian adults,” they wrote, adding that future research should focus on developing and testing low-cost, innovative recruitment and retention strategies.

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