The number of citations issued to convenience stores for selling tobacco products to minors has dramatically decreased in recent years. Between the years 1955-2000, a total of 5,511 citations were issued to convenience stores for this infraction. For the period 2000-2005, however, only 3,189 citations were issued. These statistics prove that local enforcement agencies have seriously neglected their inspection and surveillance of tobacco sales practices since 2000.
Which one of the following does the author assume in reaching his conclusion?