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Use Difference-in-Differences without an A/B test

Source: interviewintermediate

WHAT IT TESTS: causal inference when randomization is impossible. OUTLINE: give a scenario like a region-wide launch, apply Difference-in-Differences comparing treated vs control over time, and state the parallel-trends assumption.

WHAT IT TESTS: whether you can estimate causal impact when you cannot randomize, such as a feature rolled out to an entire market for legal or technical reasons. ANSWER OUTLINE: propose Difference-in-Differences, which compares the before-versus-after change in a treated group against the same change in an untreated control group, subtracting out shared trends. Its core assumption is parallel trends: absent the launch, treated and control groups would have moved in parallel.

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Use Difference-in-Differences without an A/B test · Tezvyn