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Day 1: Introduction to multi-level data problems

Day 1: Introduction to multi-level data problems

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Why would special models be needed for <strong>multi</strong><strong>level</strong> <strong>data</strong>?<br />

◮ The usual assumptions for causal inference from regression<br />

models is that individual observations are independent<br />

◮ With nested structures this may not be the case: the<br />

correlation between observations within a common unit will be<br />

higher than the average correlation of observations between<br />

units<br />

◮ Consequence is that we will underestimate the uncertainty of<br />

causal effects from pooled estimates

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