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A city implements a new speed limit (45 mph instead of 55 mph) on Highway 101 in January 2024. Researchers compare accident rates on Highway 101 to a control highway in a neighboring county that did NOT change its speed limit. Both highways have similar traffic volume and were equivalent before the policy. Accident rates are measured for 12 months before and 12 months after the policy change.
Which statement most accurately describes this design and what can be concluded?
A city implements a new speed limit (45 mph instead of 55 mph) on Highway 101 in January 2024. Researchers compare accident rates on Highway 101 to a control highway in a neighboring county that did NOT change its speed limit. Both highways have similar traffic volume and were equivalent before the policy. Accident rates are measured for 12 months before and 12 months after the policy change.
Which statement most accurately describes this design and what can be concluded?