Between 1981 and 1985, the regulatory agency overseeing pharmaceutical companies issued an average of 75 citations annually for significant breaches of drug-marketing regulations. In contrast, from 1986 to 1990, the yearly average for such citations dropped to just 10. This reduction suggests that the regulatory agency was, on average, significantly less strict in enforcing drug-marketing regulations during the latter period compared to the former. The argument assumes which one of the following?