Graphs as a tool for the close reading of econometrics (Settler mortality is not a valid instrument for institutions)
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Graphing causal models while reading econometric papers can make it easy to understand assumptions that are vague in prose and to isolate those assumptions that are crucial to believe the main causal claims. The method is here illustrated with a close reading of the paper that introduced the use of settler mortality to instrument the impact of institutions on economic development. Two causal pathways that invalidate the instrument are found not to be blocked by satisfactory strategies. The estimates in the original paper and in many that have used the instrument since should be considered highly suspect.