Contactable Non-responders Show Different Characteristics Compared to Lost to Follow-Up Participants: Insights from an Australian Longitudinal Birth Cohort Study.

Abstract

Objective This research aims to identify predictors of attrition in a longitudinal birth cohort study in Australia and assess differences in baseline characteristics and responses in subsequent follow-up phases between contactable non-responders and uncontactable non-responders deemed "lost to follow-up (LTF)". Methods 3368 women recruited from three public hospitals in Southeast Queensland and Northern New South Wales during antenatal visits in 2006-2011 completed a baseline questionnaire to elicit information on multiple domains of exposures. A follow-up questionnaire was posted to each participant at 1year after birth to obtain mother's and child's health and development information. Multivariate logistic regression was used to model the association between exposures and respondents' status at 1year. The effect of an inverse-probability-weighting method to adjust for non-response was studied. Results Overall attrition at 1-year was 35.4%; major types of attrition were "contactable non-response" (27.6%) and "LTF" (6.7%). These two attrition types showed different responses at the 3-year follow-up and involved different predictors. Besides shared predictors (first language not English, higher risk of psychological distress, had smoked during pregnancy, higher levels of family conflict), distinguishable predictors of contactable non-responders were younger age, having moved home in the past year and having children under 16 in the household. Attrition rates increased substantially from 20% in 2006 to 54% in 2011. Conclusions This observed trend of increased attrition rates raises concern about the use of traditional techniques, such as "paper-based" questionnaires, in longitudinal cohort studies. The supplementary use of electronic communications, such as online survey tools and smart-device applications, could provide a better alternative.