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Table 2 reports the full-sample regression results for our labor outcomes of interest. The effects of salt iodization on the probability of being employed (column 1) and labor force participation (column 2) are both positive and significant, with effect sizes around 0.7 percentage points for the after-by-goiter interactions. The during-by-goiter interactions in these regressions are also positive but smaller and statistically insignificant. These smaller during coefficients might be an indication that it took time for the take-up of iodized salt to spread nationwide, but we discuss evidence later (in figure 2 and table 5) that the effects of salt iodization do show up relatively quickly—just not immediately.

Table 2.
Effects of Salt Iodization on Labor and Income Outcomes
(1)(2)(3)(4)
1(Employed)1(Participated in the Labor Force)1(Worked at least 40 weeks)sinh-1(Income)
After × Goiter Rate 0.00707*** 0.00680** 0.00877** 0.105*** 
 (0.00248) (0.00284) (0.00371) (0.0290) 
During × Goiter Rate 0.00355 0.00323 0.00848*** 0.0267 
 (0.00231) (0.00233) (0.00268) (0.0259) 
Observations 2,383,143 2,383,143 1,537,003 2,135,396 
Mean of dependent variable 0.644 0.670 0.790 7.902 
(1)(2)(3)(4)
1(Employed)1(Participated in the Labor Force)1(Worked at least 40 weeks)sinh-1(Income)
After × Goiter Rate 0.00707*** 0.00680** 0.00877** 0.105*** 
 (0.00248) (0.00284) (0.00371) (0.0290) 
During × Goiter Rate 0.00355 0.00323 0.00848*** 0.0267 
 (0.00231) (0.00233) (0.00268) (0.0259) 
Observations 2,383,143 2,383,143 1,537,003 2,135,396 
Mean of dependent variable 0.644 0.670 0.790 7.902 

Standard errors, clustered by state of birth, in parentheses ***p < 0.01, **p < 0.05, and *p < 0.1. “Goiter rate” is the goiter rate in the individual's state of birth from Love and Davenport (1920), scaled by the difference between the 75th and 25th percentile of the goiter distribution (0.71). “After” is a dummy equal to 1 for those born 1928–1931. “During” is a dummy equal to 1 for those born 1924 to 1927. These regressions use the 1950–1980 Censuses, restricting to individuals born from 1920 to 1931. All regressions include state of birth fixed effects; year of birth × census year dummies; census division of birth × birth year dummies; gender; race; and during and after dummies interacted with average state latitude and 1920 state-level female and black proportions. “1(Worked at least 40 weeks)” is conditional on having worked in the past year. “sinh-1(Income)” takes the inverse hyperbolic sine of total income, including 0 s for those not working.

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