the most optimal strategy for missing data
imputation is currently not evident and it may thus be that our
strategy could have influenced the results presented. Missing values
on the primary outcomes measure were replaced using a negative
approach, in which respondents lost to follow up were regarded as
smokers. Although this approach is widely used, it might have been
too strict since many dropouts might actually have been quitters no
longer in need of the intervention, rather than smokers. Therefore,
this approach might have resulted in an underestimation of the
intervention’s effectiveness [61,62], and possibly its cost-effectiveness.
As web-based interventions have been found to be subject to
relatively large attrition rates, future research is needed to estimate
themost optimal strategy for handlingmissing data in cost-effectiveness
trials that evaluate web-based smoking cessation interventions.