Sex and age of all participants was recorded. The following covariates defined as at year of interview were also studied: (a) completed years of education (grouped as: no education, some primary, primary finished, some secondary, secondary finished, some college, and college or more); (b) relationship status (never married, previously married, married-cohabitating); (c) employment (homemaker, retired, other [including unemployed], working/student); and (d) family income (low, low-average, high-average, and high, defined via assessment of total household income, with in-country medians calculated). In the case of household income, the standard international labour economics method [31] was used to define low-income respondents as those whose after-tax household income per family member was less than half the median within their country. Low-average income was defined as up to the median income per family member in the country. High-average income was defined as income per family member above the median up to three times the median, while high income was defined as income per family member above three times the population median.
