Why 9 square miles?

 

 
 

Bell et al. used the California state Pesticide Use Report data base to categorize exposures. This database records the agricultural use of all restricted-use pesticides in the state, "including the specific chemical used, amount applied, date, and location for each application. The location is determined to the level of township, range, and section (TRS), generally representing 1 square mile." This is the limit of spatial resolution of their study.

The vital statistics database allowed them to locate the mother's residence to a TRS unit. They then determined two categories of exposure:

  • narrow definition: if pesticide use took place within the mother's TRS unit.
  • broad definition: if pesticide use took place within the mother's unit or any of the 8 units surrounding the mothers:
 
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1 sq mi
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mother's TRS
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