In Praise of the Bumps Chart III
Aug 17, 2005
Many authors have exposed and harangued statistical liars (e.g. "How to Lie with Statistics"). Likewise, I rant here once in a while. However, not every distortion of reality is unwarranted. Sometimes, distorted data actually bring out key insights. I go back to the Bumps chart to illustrate this point.
In a previous post, I remarked that the vertical axis can represent either ranking or boat locations along the river. Reading the chart from left to right as if from start to finish of the race, we suggest the right-side list displays the ending ranks or ending locations of boats.
On second thought, the right-side list cannot give us the ending locations! Physically, the boats would have moved downstream so the entire list needs to be shifted downwards to be precise. But we feel comfortable with the current arrangement: this is a distortion of reality which does not affect our reading ability. Indeed, it enhances our ability to see into the data because now a horizontal line means no change in ranks.
If one is very particular, then one should interpret the right side as next year's starting locations rather than the current year's ending locations. Then all is well.
In many situations, reducing continuous data to ranks introduces significant distortion and is thus not advisable. For the Bumps chart, because the Bumps rules require that all boats start next year the same distance apart, in essence wiping out the year-end separations, the form perfectly fits the function! This distortion removed information not needed to grasp the key point of the chart, so no harm done!
As a side note -- Tim Granger has produced a side-by-side Bumps chart, even more marvellous than the single-period chart. In my junkart version, I removed the horizontal line segments linking one year to the next. These line segments contain no data; besides, based on the discussion above, each right vertical axis should be interpreted as next year's starting locations rather than this year's ending locations, so these line segments are unnecessary.
PS. In case you're wondering, Tim colored some lines red to indicate boats that managed to bump up each of the four days in a specific year. These teams win an award called the "blades". If the purpose of the chart is to identify the rise and fall of boat club dynasties then we would have colored the trajectory of Pembroke (6) and Queens (19), for example.
A reader, John, alerted me to the black boxes that appear when you click on the images. I have fixed them. In the future, I'm going to make the images bigger so there is less clicking. Thanks John!
Posted by: Kaiser | Aug 21, 2005 at 11:35 AM