n><mo>,</mo><mi>…</mi><mo>,</mo><mi>K</mi></mrow><annotation encoding="application/x-tex">k = 1, \dots, K</annotation></semantics></math>,
<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><msub><mi>γ</mi><mi>k</mi></msub><annotation encoding="application/x-tex">\gamma_k</annotation></semantics></math>,
systematically differ from the mean effect, with the variance of the
district-level effects summarized with heterogeneity
<math display="inline" xmlns="http://www.w3.org/1998/Ma