Figure 2.

Multivariate relationship between percent emphysema and mean activity count in a centered scatterplot and generalized additive model with local regression smoothing (LOESS) plot. Centered scatterplot and LOESS plot with 95% confidence interval and smoothing parameter of 0.6. Fully adjusted model includes age, sex, race/ethnicity, education, scanner manufacturer height, weight, BMI category, FEV₁, cotinine level, and pack-years (n = 1,316). The P value for the main association = .003. The deviation for nonlinearity was nonsignificant (P= .32). Excluding high percent emphysema values above the 95th percentile shows similar results (main association coefficient, −4.4; P = .002; nonlinearity P = .28; graph not shown). In a second generalized cross-validation model using the prediction of the sum of squares (df = 0.97), the P value for the main association was .001, and the deviation for nonlinearity stayed nonsignificant (P = .34; graph not shown).