Monday's Lesson

Today's lesson is a lesson in reading graphs. The lesson to be learned is to read graphs carefully. And never take them at face value, especially if someone's selling something. (My real rant is the link in the last paragraph, if you want to skip the lesson and get straight to the payoff.)

For example, changing the scale on a graph can make it look totally different. Zooming in on a graph makes any differences or changes appear larger, so you might want to use this to exaggerate how much better your product is than the competitor's or how much something has changed with time. From the beginning to the end of this graph, the value has doubled (100 to 200), but the way it is graphed makes it look three and a half times as big (40 to 140 above the axis).

Logarithmic graphs can be used to diminish the impact of large values compared to small values, or just to clarify when several orders of magnitude are involved. Imagine this graph on a linear scale! Within a few months, it would be indistinguishable from zero.

Even more egregious ways to play with the axes of a graph include leaving a break in the axis or rescaling the axis part way through. Both of these things appear to be done here to make it look like there is a pattern in the data that doesn't actually exist.