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Properties of the Cigarette Dependence Scale and the Fagerström Test of Nicotine Dependence in a representative sample of smokers in Norway.

AIMS
To compare the properties of four measures of dependence to nicotine/tobacco, the 12-item Cigarette Dependence Scale (CDS-12), the six-item Fagerström Test of Nicotine Dependence (FTND) and two shorter versions of the same measures.


METHODS
In a cross-sectional telephone survey of smokers in a representative general population sample in Norway, we compared the measures. We assessed (i) internal consistency reliability with Cronbach's alpha; (ii) compared item scores; and (iii) tested the validity of the questionnaires. Test-retest reliability was assessed in a smaller convenience sample.


RESULTS
Among 1265 respondents (64%), 290 (23%) were daily smokers and included in further analysis. Their mean age was 42 years [standard deviation (SD) 15] and 46% were female. They smoked on average 13 cigarettes per day (SD 6). Internal consistency reliability was 0.61 for the FTND (n = 267) and 0.81 for the CDS-12 (n = 266). Score distributions suggested a floor effect for the FTND. Test-retest reliability was 0.90 for the FTND and 0.97 for the CDS-12 (n = 31). The correlation between the scale scores and a question about the maximum willingness to pay for a cigarette after not smoking all day was 0.36 (P < 0.001) for the FTND (n = 262) and 0.45 (P < 0.001) for the CDS-12 (n = 263). There was little difference in the associations of the two scales or their abbreviated versions with external variables.


CONCLUSIONS
Telephone administration was acceptable for both questionnaires, and we have established population reference values for the four scales. The questionnaires were associated with each other and showed similar properties. The findings support the construct validity of the scales.