![]() ![]() ![]() ![]() If you have both x and y values (say, test scores and the years in which those scores were reported), you want "Scatter Plot," which will properly space the data on the horizontal axis. As I tell my intro physics students over and over, though, "Line Plot" is never the right choice, because of this exact problem. These points are plotted at regular intervals because Kevin used Excel to make the graph (the ugly colors are another dead giveaway), and did what looks like the reasonable thing to do when you want to plot lines connecting your data points, namely choosing "Line Plot" from the plot options Excel offers. If you actually read the labels, though, you'll see that they're anything but regular- the first few points show test scores at four- or five-year intervals, then there's a cluster of two-year intervals, then some more long gaps. If you look at the horizontal axis of this plot, it shows regularly spaced intervals. This shows test scores for black students in various age groups over time, but more importantly, it demonstrates one of my pet peeves about Excel. I was pulling them together this morning to do a sort of themed links dump, when the plot at the right, from Kevin Drum's post about school testing jumped out at me. There have been a bunch of interesting things written about education recently that I've been too busy teaching to comment on. ![]()
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