Figure 2. Unadjusted regression lines for weight change tertiles in women (n = 1,577).

11-year weight change was divided in three groups, a lower, middle and upper tertiles. In the adjusted regression model, regression coefficients (β) for the association between Δfree T4 and ΔTSH differed significantly in the three groups (P<0.0007 for the interaction between Δfree T4 and Δweight tertiles), and was estimated to: β_{lower Δ weight tertile} = −0.047 mU/L (CI, −0.096, −0.0018), β_{middle Δ weight tertile} = −0.049 mU/L (CI, −0.093, −0.005), and β_{upper Δ weight tertile} = −0.150 mU/L (CI, −0.191, −0.109). Note the lines of the lower and middle weight change tertiles are difficult to distinguish from each other. Adjustments were made for age group (categorical), change in smoking status, change in leisure time physical activity, and for the baseline value of the outcome.