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Authors' reply

Published online by Cambridge University Press:  02 January 2018

Rajeev Krishnadas
Affiliation:
Sackler Institute of Psychobiological Research, University of Glasgow, Southern General Hospital, Glasgow G51 4TF, UK. Email: Rajeev.Krishnadas@glasgow.ac.uk
Sameer Jauhar
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, King's College London
Susan Telfer
Affiliation:
Coathill Hospital, NHS Lanarkshire
Somashekara Shivashankar
Affiliation:
Cardiff and Vale University Local Health Board, Psychiatry, Cardiff
Robin G. McCreadie
Affiliation:
Crichton Royal Hospital, Psychiatry, Dumfries, UK
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Abstract

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Columns
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Copyright © Royal College of Psychiatrists, 2013 

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. Reference Steinberg, Williams, Steinberg, Krejci and Ziedonis1 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. Reference Radzius, Gallo, Epstein, Gorelick, Cadet and Uhl2 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. Reference Darlington3 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. Reference Rummel4 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. Reference Patkar, Gopalakrishnan, Lundy, Leone, Certa and Weinstein5 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. Reference Miller and Chapman6

References

1 Steinberg, ML, Williams, JM, Steinberg, HR, Krejci, JA, Ziedonis, DM. Applicability of the Fagerstrüm Test for Nicotine Dependence in smokers with schizophrenia. Addict Behav 2005; 30: 4959.CrossRefGoogle ScholarPubMed
2 Radzius, A, Gallo, JJ, Epstein, DH, Gorelick, DA, Cadet, JL, Uhl, GE, et al A factor analysis of the Fagerstrüm Test for Nicotine Dependence (FTND). Nicotine Tob Res 2003; 5: 255–40.CrossRefGoogle ScholarPubMed
3 Darlington, RB. Factor analysis. Available online at: http://comp9.psych.cornell.edu/Darlington/factor.htm.Google Scholar
4 Rummel, RJ. Applied Factor Analysis. Northwestern University Press, 1970.Google Scholar
5 Patkar, AA, Gopalakrishnan, R, Lundy, A, Leone, FT, Certa, KM, Weinstein, SP. Relationship between tobacco smoking and positive and negative symptoms in schizophrenia. J Nerv Ment Dis 2002; 190: 604–10.CrossRefGoogle ScholarPubMed
6 Miller, GA, Chapman, JP. Misunderstanding analysis of covariance. J Abnorm Psychol 2001; 110: 40–8.CrossRefGoogle ScholarPubMed
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