FIGURE 2.

Age, period, and cohort effects on the probability that US adolescents regularly report ≥7 hours of sleep per night from 1991 to 2012 in nationally representative samples (N = 270 899). The cohort and period time–scale contains risk ratio estimates for the effect of cohort (far left line) and period (far right line). Thin lines indicate 95% confidence intervals. The cohort estimates were compared with a referent cohort of 1980; thus, the lines can be interpreted as the average proportion of adolescents obtaining ≥7 hours of sleep regularly, regardless of time period, compared with the average proportion in 1980. The period estimates were compared with a referent period of 1995; thus, the lines can be interpreted as the average proportion of adolescents obtaining ≥7 hours of sleep regularly in that year, regardless of cohort, compared with the average proportion in 1995.