I came across this chart on the Interweb recently (copied exactly as shown on a school website):
It's not clear what story this chart is attempting to tell, but I think it's safe to assume that the purpose of the visualisation is to demonstrate those form groups with the lowest attendance and to allow some form of comparison across a year group and across the whole school. I think the chart fails in a number of ways.
- The chart starts at 70% - this magnifies the visual perception of the difference between any two forms -- the chart is stretched vertically and this distorts our visual understanding of the data
- Whilst it is possible to pick out the form (10PW) with the lowest attendance overall, it is not clear how this relates to other Year 10 classes or overall
- The x-axis contains categoric data
- There is no context for this chart - we dont know what a "good" or "target" value is.
Some Excel-fu later and you can transform that chart into: