The importance of plausible data-generating mechanisms in simulation studies: A response to 'Comparing methods for handling missing covariates in meta-regression' by Lee and Beretvas (doi: 10.1002/jrsm.1585).

The paper by Lee and Beretvas (doi:10.1002/jrsm.1585) described a well-executed simulation study comparing 'modern' with 'ad hoc' methods for performing meta-regression when some covariates are incomplete. However, they drew practical conclusions after simulating data under a single missing data mechanism which favoured the 'modern' methods, while other missing data mechanisms would have favoured the 'ad hoc' methods. Broad recommendations about methods to use in practice should instead be based on simulation studies using a range of plausible data-generating mechanisms. This range must represent what is believed likely to occur in practice, and not what is convenient for statistical analysis.