Fig. 4 graphically assesses the validity of this paper’s approach
by testing whether predicted life expectancy, calculated as the
fitted value from an ordinary least-squares (OLS) regression of life
expectancy on all covariates except TSPs (just as in Table 1), differs
at the Huai River’s border. Specifically, this equation includes
all of the covariates listed in panels 2 and 3 of Table 1, and these
variables collectively explain a substantial portion of the variation
in life expectancy (R2 = 0.265). It is evident that predicted life expectancy
is essentially equal just to the north and south of the border
(Table 1 reports a P value of 0.81 from a test of equal life expectancy).
Also note that SI Appendix, Table S2 demonstrates that dietary
and smoking patterns are similar in the North and South,
suggesting that these determinants of life expectancy are unlikely to
explain the sharp decline in life expectancy north of the border.