Graphing Grade Inflation

June 5, 2013
Posted by Jay Livingston

I have little talent in the visual arts.  But since I started doing this blog, and especially when Sociological Images started using some of my posts, I’ve become more sensitive to graphs. and the visual presentation of quantitative data.  In the old days, when I had trouble deciphering a graph, I blamed my own visual limitations.  Now, I think about how the graph might be improved. 

A couple of days on a campus listserv, someone posted this graph to illustrate grade inflation.

The first comment on this began, “If I understand the chart correctly . . .”  Exactly.  The chart is hard to understand. When you are trying to show changes over time, lines flowing from left to right imply that time sequence, so this graphs makes it seem as though F’s were changing to D’s and then to C’s, and so on.  When I wanted to know how the percentage of B’s had changed over the three time-points, I had to keep looking at the legend to see which color dot represented each year.

Was there a better way to graph the 30 data points?  This is what I came up with.

I thought it was better.  But the first comment on it said, “I like the earlier one and actually find it easier to make comparisons across institutions.” 

1 comment:

Bob S. said...

I can see the inflation of the upper grades easily in the second graph.

The first graph really pops out if anyone understand the normal distribution of things.

I would put the public/private graphs side by side in the second graph, grouped by years.

Then the differences in inflation would be seen to be across the years not the type.

Visualization of data is difficult; congrats for your efforts to improve.