Jabberwalker Jabberwalker:
Iodized salt is so ubiquitous that you couldn't possibly run a controlled experiment about it. All sorts of influences could have raised IQs in the twenties .. like improved nutrition, health care, for instance.
I wonder if they crashed again in the Thirties when a hoards of people had to "go without".
Said no one who read the study.
$1:
Our identification strategy relies on two important sources of variation. The first is the pre-existing extent of underlying iodine deficiecy. In regions where goiter was low among men drafted in WWI, we expect little change after iodizing salt. In regions where goiter was high we expect to see a significant increase in the proportion of men being assigned to the Army Air Forces after iodizing salt. Our second source of variation arises from the timimg of the intervention. The rapid introduction of iodized salt provides for a clean distinction between the treated and the untreated. We expect to see a sharp di erence between cohorts born before and after 1924. High goiter areas therefore provide the treatment group and low goiter areas the control group. Years before 1924 are pre-treatment and years after 1924 are post-treatment.
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