How much loss to follow-up is acceptable in long-term randomised trials and prospective studies?

• Published in: Archives of disease in childhood Vol. 93; no. 6; pp. 458 - 461
• Main Authors: Fewtrell, Mary S, Kennedy, Kathy, Singhal, Atul, Martin, Richard M, Ness, Andy, Hadders-Algra, Mijna, Koletzko, Berthold, Lucas, Alan
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group Ltd and Royal College of Paediatrics and Child Health 01.06.2008; BMJ Publishing Group Ltd; BMJ Publishing Group LTD
• Subjects: Adolescent; Adult; Attrition (Research Studies); Child; Child, Preschool; Clinical trials; Cohort analysis; Company business management; Data Interpretation, Statistical; Developmental Disabilities - etiology; Developmental Disabilities - prevention & control; Disease; Evidence; Evidence-based medicine; Evidence-Based Medicine - standards; Evidence-Based Medicine - statistics & numerical data; Female; Follow-Up Studies; Funding; Humans; Infant; Infant, Newborn; Influence; Male; Management; Nutrition; Outcome Measures; Patient compliance; Patient Dropouts - statistics & numerical data; Pediatric research; Physiology; Population; Practice Guidelines as Topic; Pregnancy; Prenatal Nutritional Physiological Phenomena; Programming; Prospective Studies; Randomized Controlled Trials as Topic - standards; Randomized Controlled Trials as Topic - statistics & numerical data; Reporting requirements; Studies; Validity; Young Children
• ISSN: 0003-9888; 1468-2044; 1468-2044
• DOI: 10.1136/adc.2007.127316

Many cohorts enrolled people who were born in the first half of the 20th century, and it is possible that the nature and size of any associations are different in contemporary populations. [...]although these studies have generated considerable interest they have been unable to examine direct associations with diet or establish whether associations are causal and cannot, therefore, be used to inform infant feeding recommendations. In RCTs, typically investigating drugs or other therapies, it has been suggested that a loss to follow-up <=5% is usually of little concern, whereas a loss of >=20% poses serious threats to validity, with in-between rates leading to intermediate levels of problems. 1 Indeed, a cut-off of 80% is used in Evidence-Based Medicine (EBM) "Levels of Evidence" to separate "high"- and "low"-quality randomised trials. 2 This figure is based on the concept of being able to detect a hypothesised difference between randomised groups at follow-up after applying the "worst case scenario" for missing data - that is, assuming that subjects lost to follow-up from each arm of the study have the outcome seen in the other limb.