Applied Epistemology

On one of my last quizzes of the semester in critical thinking, I give the following example of bad reasoning (taken almost verbatim from a real think tank report I found on the web):

In 1964, when the bracero program ended, 86,597 people were apprehended by the INS for illegal immigration. In 1976, INS apprehensions were 875,915—a more than 1,000% increase. This indicates there was a significant rise in illegal immigration.

I have asked this question for a few years now. But only this semester did I get the following response:

"This is a weak argument. The 1000% number seems bogus; where did it come from."

Aieee!!!!