Attrition analysed in five waves of a longitudinal yearly survey of smokers: findings from the ITC Netherlands survey.

Background: Attrition bias can affect the external validity of findings. This article analyses attrition bias and assesses the effectiveness of replenishment samples on demographic and smoking-related characteristics for the International Tobacco Control Netherlands Survey, a longitudinal survey among smokers.

Methods: Attrition analyses were conducted for the first five survey waves (2008-12).