Age was categorized into six groups: 18–27, 28–37, 38–47, 48–57, 58–67 and 68+ years. With respect to educational achievement, individuals were categorized into one of four groups: no high-school diploma or GED, high-school diploma or GED only, some college or other post-secondary education but not a bachelor’s degree, bachelor’s degree or higher. Subjects from each survey were grouped into quartiles defined by total household income. Quartiles were defined separately for each survey, and cut-offs were determined by ranking of un-weighted data.
