Is attrition bias a problem in neonatal follow-up?

Abstract

Aim: To assess whether attrition rate influences outcome in the follow-up of very preterm infants.

Study design: In a national follow-up study of infants born alive in 1983 in the Netherlands with a gestational age less than 32 weeks and/or a birth weight less than 1500 g, outcome was assessed separately for adolescents who responded early or late to a follow-up invitation at age 14 years. Neonatal data and outcome results of earlier assessments from early and late responders were compared to those of non-responders by univariate and nominal (polytomous logistic) regression analysis.

Subjects: There were 723 (76%) early responders, 130 (14%) late responders and 109 (11%) non-responders.

Results: We found significantly more non-Dutch origin and more disabilities and school problems at age 10 years in late- and especially in non-responders. At age 14 years, the health utility index was significantly lower in late responders compared to early responders. School outcome did not show difference in relation to the response groups.

Conclusion: The results suggest that the incidence of adverse outcome in very preterm infants is underestimated when follow-up is incomplete and hence response rate is not a negligible problem in the assessment of late outcome. Therefore, follow-up studies should include a drop-out analysis to enable comparison to other studies.