As data were collected on more than one occasion for some individuals, the composition of the dataset could vary. Two compositions were examined. In both cases, telephone interview data were selected over mailed questionnaire data. Telephone interview data collected on two occasions were available for 1533 individuals, with a mean time between interviews of 8.2 years (SD = 3.1 years, range 1–13 years). One dataset maximised data collected from older individuals by selecting the most recent telephone interview data, whereas data from earlier interviews were selected for the alternative dataset, thus maximising data from younger individuals. Table 1 shows participant numbers and age for the different data collection phases and for each dataset composition. Test-retest correlations for the 1533 retested individuals were 0.51 for Quantity × Frequency, 0.48 for Quantity, and 0.58 for Frequency.
