A city implemented a new traffic regulation, and a year later, reported a 15% decrease in traffic accidents. City officials claimed the regulation directly caused the reduction. Which of the following, if true, would most weaken the city officials' claim?

✓ Correct Answer: Option A

If traffic volume significantly decreased, fewer accidents would naturally occur, regardless of the regulation. This introduces a confounding variable that provides an alternative explanation for the observed reduction, weakening the claim of direct causation by the regulation.