Slope charts are often suggested as a valid alternative to clustered bar charts, especially for “before and after” cases.
So, instead of a clustered bar char like this
we tend to recommend a slope chart (or slope graph) like this
However, a slope chart isn’t free of problems either. In the past, I already wrote about a case of a meaningless slopegraph [here]. Today, I stumbled upon an interesting blog post (and a video) that surveys the problems of slope chars and their alternatives
All the graphs here come from the original post by Nick Desbarats that can be found [here].
That fact that you can doesn’t mean that you should! I will say it once again.That fact that you can doesn’t mean that you should! Look at this slopegraph that was featured by “Information is Beautiful”
What does it say? What do the slopes mean? It’s a slopegraph, its slopes should have a meaning. Sure, you can draw a line between one point to another but can you see the problem here? In this nonsense graph, the viewer is invited to look at slopes of lines that connect dollars with years. The proverbial “apples and oranges” are not even close to the nonsense degree of this graph. Not even close.
This page attributes this graph to National Geographic, which makes me even sadder.