Data Collectionhard
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A city implements a smoking-reduction policy on January 1, 2025. Monthly smoking prevalence data:

Before: Jan-Dec 2024: 22%, 22%, 21%, 21%, 20%, 20%, 20%, 20%, 19%, 19%, 19%, 18% (relatively flat, slight trend)

After: Jan-May 2025: 16%, 15%, 14%, 12%, 10% (sharp decline)

An interrupted time series (ITS) analysis fits separate regression lines before and after the policy date. What does ITS primarily estimate?