Authors' reply

We agree with Basu & Nebhinani that recent studies have questioned the psychometric properties of the FTND in this population. Indeed, as Steinberg et al suggest, we may have underestimated nicotine dependence by using the FTND. ¹ We acknowledged this shortcoming in the article. We conducted a principal components analysis on our data-set, in accordance with Steinberg et al. Our results revealed a two-factor structure similar to that of Radzius et al, explaining 53% of the total variance. ² The first factor reflected the degree of urgency to restore nicotine levels after night-time abstinence, and the second factor reflected the persistence with which nicotine levels are maintained during waking hours, thereby tapping into different domains of nicotine dependence itself. This is in contrast to Steinberg et al, who found two factors that were non-meaningful. In addition to other limitations acknowledged by Steinberg et al, exploratory factor analysis techniques have a number of methodological concerns. Most importantly, interpreting the results of any exploratory analyses like principal components analysis is heuristic and may not necessarily reflect the truth in the given data. ³ This is probably one of the reasons why studies that have used such approaches have shown inconsistent factor structure for the FTND, even in non-psychiatric samples. Such studies should be interpreted with caution. In addition, as Basu & Nebhinani rightly point out, reducing a complex, overlapping and holistic concept such as dependence to a few simple meaningful factors may not be theoretically correct or possible. ⁴ At a pragmatic level, a measure such as pack-years (which only measures amount and duration of smoking) may be a useful measure of lifetime nicotine consumption. We are, however, unaware of any studies that have validated the FTND (or its modifications) or pack-years using a gold standard diagnostic criterion for nicotine dependence in the schizophrenia population. The closest we came was Patkar et al, who found a significant correlation (r = 0.89) between the FTND scores and DSM-IV diagnosis of nicotine dependence. ⁵ Although it is possible that psychopathology may have affected the FTND scores, in our study, the scale administration was facilitated by two clinicians (S.S. and S.T.) thereby lending some objectivity to the measurement.

All participants gave written informed consent. We considered antipsychotic type as a covariate in the model. With regard to other potential confounding factors, our relatively small sample size meant that we did not have enough power to stratify the sample or to add more covariates into the model. It should, however, be noted that adding variables that may themselves significantly covary with nicotine dependence (independent variable) – such as smokeless nicotine/substance use and physical comorbidity – would, in view of controlling for their effects, have decreased the variance explained by nicotine use itself and therefore have been deemed inappropriate in this setting. ⁶