INSERM, UMR S 720, Paris, F-75013, France.
Comparing different genotypic interpretation systems is of interest to improve knowledge of the relationship between resistance mutations and virological response under a specific drug. The motivation for choosing a specific system should be based on comparison using appropriate statistical methods. There is some confusion as to the correct use of the linear regression model with its R(2) measure in this setting, especially when models using a single discrete variable are compared with a model using many variables.