Fig. 2

Generalized additive regression. (A) GAM for total population BRI; (B) GAM for male BRI; (C) GAM for female BRI. (D) GAM for total population WWI; (E) GAM for male WWI; (F) GAM for female WWI. Note: The BRI had a nonlinear positive relationship in the total population, with an inflection point of 4.36 and no sex difference. WWI had a nonlinear positive relationship in the total population, with inflection points of 10.69 and 11.89 in the total and male populations, respectively.