These coefficients assume, possibly incorrectly, that the same relative-odds hold throughout the life course and linearly across the age range of respondents at the time of interview, but simplifying assumptions of these sorts are needed to grasp such a wide range of associations all at once. These assumptions are investigated next, but within the context of these limitations, the data are clear in showing that the dominant tendency in the data across countries, and across drug types, is for risk to have increased over historical time, defined by the life courses of the respondents in these surveys.
