Wednesday, August 31, 2011

The Chicago Tribune is unprepared for college

The Chicago Tribune published today an article with a plausible headline --- public high school students are unprepared for college --- but their logic is suspect. A state law required public universities to publish the average freshman year GPAs for students from each high school, and the Tribune has published their interpretation of the data. For each university, the Tribune plotted the high school grade point averages (GPAs) of incoming students versus their average GPA in colleges. They conclude that if students have a lower GPA in freshman year of college than high school, that implies that students were unprepared.

It seems obvious to me that college GPAs are lower than high school GPAs. About 50% of Harvard students were ranked 1 or 2 in their high school graduating class, and probably over 80% had a GPA of 4.0, and yet college GPAs are way lower. Further, college GPAs come from a wide variety of courses, so they're even harder to interpret than high school GPAs. Engineering students have lower GPAs than humanities majors, so a really good high school that sends most of its students to major in engineering might look worse than a mediocre high school that sends most of its students to major in humanities. If college GPAs weren't lower than high school GPA, I would think that the students weren't challenging themselves enough. Finally, high schools with disadvantaged students can be expected to have lower college GPAs not because the students are poorly prepared by their high schools but because the students were disadvantaged.

The report itself is more useful, and it provides a good comparison of the students from each high school that tend to attend each school. Not a comparison of the high schools themselves, of course: enormously confounded by the which students from each school tend to attend the state universities. It does break down GPA by subject. A high school that sends its best students to the University of Illinois at Urbana-Champaign will look like a better high school who sends its best students out of state. Still interesting.

The Tribune's assumption that having a lower GPA in freshman year of college than high school implies that students weren't prepared conflates many issues in an illusion that a few numbers can summarize a high school without any statistical assistance. Is this a reminder that a weak attempt at evidence-based decision-making is worse than none at all?

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