CAUSAL-INFERENCE5 MIN READ
Test the Parallel Trends Story
Evaluate whether a rollout can support a DiD-style causal read.
The rollout Phoenix received weekend staffing; Denver did not. The causal read depends on what Phoenix would have done without the staffing change. Difference-in-differences Parallel trends, not equal levels The comparison group must represent the untreated trend for the treated group. Pre-trends are the first credibility check. 01 Pre-trend 02 Shocks 03 Try Step 1 Phoenix backlog was falling faster than Denver before staffing changed. What is the strongest first response? Other shocks Step 2
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