This chart appeared on a blog post saying auto sales are “down again” and this should worry us about a recession. See that blue arrow at the right? Looks horrible!!!!
But this chart design is a real mess.
First, the blue arrow anchors our view on the blue line and its downturn at the right. But the real chart is the harder to see gray column chart. Column charts are a *terrible* way to show a trend – line charts work much better.
The blue arrow and the blue line is what we see when we look at this chart – but it is the gray columns that show the trend the original writer was referencing!
But look closer. Over 80% of the length of that down arrow, truck sales were growing – and truck sales make up the majority of vehicle sales. The miscolored blue arrow was anchoring our thought processes inadvertently to the truck sales – when it should have been a gray arrow to link us to the columns (which again, are a terrible way to show a trend) – what a mess!
Now look even closer. Truck sales are down during the winter and spring every year:
From merely eye balling the chart, you can see that this years sales drop is less than the prior years sales drop.
Truck sales, are more than 50% of all “auto sales” and every every spring, they drop in a cyclical fashion.
What the chart shows is that truck sales, which are the majority of total auto sales, are doing well. Overall “total auto sales” for May 2016 are greater than May of 2015, although in between sales went still higher and then dropped back.
This chart “works” due to the use of “anchoring” on the blue line and failing to compare sales year-over-year, which rise and fall in a non-linear manner due to seasonal effects.