FIGURE 2 Linear regression coefficients (95% CIs) showing the difference in mean waist circumference between 1999–2000 and each subsequent study.
Differences were estimated by using a logistic regression model that included the study cycle as a 7-level categorical variable with 1999–2000 as the reference category. Black circles and solid lines denote estimates from models that included race and age, whereas open triangles are estimates from models that included BMI as an additional predictor. Age and BMI were modeled by using restricted cubic splines with 4 knots, and 2-factor (linear) interactions between age, BMI, and race-ethnicity were included in the BMI-adjusted model