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Using Trellis Charts to Display Small Multiples Over Time

Mike Cisneros shows us the evolution of three-point shooting in the NBA using a trellis chart:

 This small multiple chart shows two variables for each team in the league for each of the last 30 seasons: on the x-axis, the number of 3-pointers attempted per game; on the y-axis, the percent of attempted 3-point shots that were successful. Each point is a single team in a single season. The individual panels step you forward in time as the data changes and evolves. They help you see how the pack of all NBA teams is inexorably moving towards more and more 3-point attempts per game (the data points shift rightwards as you progress through the frames). We can also see that there are no longer any teams with sub-30% shooting percentages on those attempts (illustrated by tighter clustering upwards as you move forward in time).

This is a good way of showing movement over time in a static medium, like a printed page. If you’re giving a presentation, this would probably be a bubble chart with a play axis.

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