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Table 1 Description and examples of mechanisms through which external factors can impact SWD studies

From: Accounting for confounding by time, early intervention adoption, and time-varying effect modification in the design and analysis of stepped-wedge designs: application to a proposed study design to reduce opioid-related mortality

Scenario Description Example
Confounding by calendar time External factors that vary over time and affect the outcome independently of the intervention under study Statewide policies limiting initial opioid prescriptions to a 7 day-supply
Early intervention adoption (noncompliance) Partial or full adoption of the intervention before its scheduled roll-out time; such events differentially impact intervention and control clusters Use of opioid overdose reversal medication, naloxone, by first responders prior to the scheduled roll-out time for the community
Time-varying effect modification External factors that differentially impact the outcome overtime; depending on whether or not they are receiving the intervention Changes in insurance policies to limit access to standard opioid treatments