In the city of Cantville, a high school earns the “Young Women in Science” award for a given year if at least ten of its female students participate in that year's state science exposition. Last year, 80 percent of all high schools in Cantville's District 1 earned this award, while only 63 percent of all high schools in the city's District 2 earned the same award. Furthermore, these percentages have remained at or near those respective levels throughout the entire twelve years since the award was instituted. It is clear, then, that the high schools in District 1 do a better job of encouraging girls to pursue science than do the high schools in District 2.

Which of the following is assumed in the argument above?