One guaranteed to make Stephen Few cry

Vox published this chart:

This sort of chart is, unfortunately, quite common in business circles. Just about the only thing one can read readily from this chart is the overall growth in the plug-in vehicle market (the heights of the columns). 

To fix this chart, start subtracting. First, we can condense the monthly data to quarterly:

This version is a bit less busy but there are still too many colors, and too many things to look at.

Next, we can condense the makes of the vehicles and focus on the manufacturers:

This version is still less busy and more readable. We can now see Chevrolet, Nissan, Toyota, Ford and Tesla being the five biggest manufacturers in this category. All the small brands have been aggregated into the "Others" category. The stacked column chart still makes it hard to know what's going on with each individual brand's share, other than the one brand situated at the bottom of the stack.

Next, we switch to a line chart:

This shows the growth in the overall market, as well as several interesting developments:

• The growth in the number of competitors in the market especially since 2012
• The fragmentation of the market. Before mid 2012, Chevrolet was dominating the market. Since then, there are five or six brands splitting the market
• The first-to-market brands have not been able to sustain their advantage

A smoothed version of the line chart is even more readable:

Graphics is a discipline that often rewards subtracting. Less is more.

***

In the above discussion, I focused on the Visual aspect of the Trifecta Checkup. This dataset is really difficult to interpret, and I'd  not want to visualize it directly.

The real question we are after is to assess which manufacturer is leading the pack in plug-in vehicles.

There are a number of obstacles in our path. Different makes are being launched at different times, and it takes many months for a new make to establish itself in the market. Thus, comparing one make that just launched with another that has been in the market for twelve months is a problem.

Also, makes are of different vehicle types: compacts, SUVs, sedans, etc. More expensive vehicles will have fewer sales whether they are plug-ins or not.

Thirdly, population grows over time. The analyst would need to establish growth that is above the level of population growth.