GMAT Critical Reasoning (CR) | Re: A report of a government survey concluded that Center City was among

A report of a government survey concluded that Center City was among the ten cities in the nation with the highest dropout rate from its schools. The survey data were obtained by asking all city residents over the age of 19 whether they were high school graduates and computing the proportion who were not. A city school official objected that the result did not seem accurate according to the school's figures.

The school official can most properly criticize the reasoning by which the survey