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. 2010 Mar 8;118(9):1318–1325. doi: 10.1289/ehp.0901315

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Flow chart of stratification approach. Six steps: input variables h1–h3, a1–a5; indices H, A; spatial scales; and rules used. Abbreviations: avg, average; pop, population; _T denotes town scale; _TS standardized town scale.