that haplotype proportions change linearly across the response options. The only nominally significant results were obtained in the early onset condition for cigarettes per day (Item 4), Cochran's Test of Linear Trend (1, N = 1499) = 16.6, p<0.00005, and for early morning smoking (Item 5), χ2 (1, N = 1142) = 4.01, p<0.05. In sum, the pattern of findings suggests that multiple items contribute, albeit modestly in some cases, to the measurement of nicotine dependence as it is associated with haplotypes. Since the items of the FTND are not highly correlated with one another, the additive effects of the different items have the potential to yield orthogonal variance and a more comprehensive assessment of nicotine dependence than is available via only a subset of items [2].
