Construct validity of the Smoker Complaint Scale: A clinimetric analysis using Item Response Theory (IRT) models

A number of rating scales evaluating symptoms of nicotine withdrawal have been developed over the years but insufficient attention has been devoted to the assessment of their clinimetric properties. Clinimetrics, the science of clinical measurements, is an innovative approach, particularly useful for assessing the validity of rating scales. This is the first study using clinimetric principles to test the construct validity of the Smoker Complaint Scale (SCS), a self-rating scale specifically developed to assess acute symptoms of nicotine withdrawal. Construct validity was evaluated via Item Response Theory (IRT) models (i.e., combining Rasch and Mokken analyses). A total of 366 subjects (mean age = 34.0, SD = 11.3 years) participated in the study. IRT analyses showed that SCS was a multidimensional measure of symptoms of nicotine withdrawal, including unidimensional subscales, particularly a four-item subscale (the SCS₄), which was found to entail the clinimetric property of construct validity. IRT analyses also revealed that affective symptoms of nicotine withdrawal preceded cognitive ones. The SCS should be considered as an item bank, including a particularly valid subscale, the SCS₄ that can be used as a screening or outcome measure to evaluate the severity of cognitive and affective symptoms of nicotine withdrawal. SCS₄ is a sensitive clinimetric index which differentiates "ceiling symptoms" of nicotine withdrawal (e.g., "feeling slowed down") from "floor symptoms" of nicotine withdrawal (e.g., "feeling lightheaded") that emerge in the severe form of nicotine withdrawal.