Being a bit of a Stephen Few fan, I’ve now absorbed his latest book, Now You See It: Simple Visualisation Techniques for Quantitative Analysis.
Unlike everyone else (yes everyone) who has reviewed it on Amazon.com so far, I don’t actually think it deserves a full 5-Star rating on all fronts (for instance, the reproduction of Tableau charts and some other outputs is low in terms of image quality, which for a visualisation publication surely is a problem). That aside however, it does have some excellent content and one particular device which I’ve latched onto is contained in the chapter on Distribution Analysis.
Representing a metric and providing information on the value relative to the entire distribution is having your cake and eating it. Not only do you get the measure, but you see where it sits relative to its peers so I see this as a very complimentary graphic alongside the more traditional metric traffic light and trend presentation.
So what could a metric distribution analysis look like?
Few uses an example where you have the Low, Median and High values of a particular measure displayed on a single axis, he then improves the example by adding a marker for the 25th and 75th percentiles.
This then starts to sound very similar to the tertile distribution (where we chop the data up into thirds) we have been working on for presenting unit and course metrics at UNE. We have calculated a lower, mid and upper tertile with boundaries at 33.34% and 66.67%. Each measure for each unit and course is then calculated and given the appropriate traffic light depending on which tertile it falls into.
What we hadn’t thought of was being able to supplement the traffic light, trend and value with a distribution chart. So here’s how it currently looks in development for a sample unit for our Attrition measure based on Few’s ideas:
- Attrition is less than 10% for this unit (green star)
- The lowest attrition of any unit is just under 5% (left red triangle)
- The 33rd percentile is at around 14% attrition (blue vertical bar)
- The 66th percentile is at around 22% attrition (light brown vertical bar)
- The highest attrition of any unit is around 31% (right red triangle)
- This unit is performing very well and attrition is significantly low
In combination with the traffic light, trend and time-series line chart, there is a huge amount of information being conveyed by a very simple instrument. Should I add values to this? Well maybe. I tried and it got really cluttered and of course the traffic light scorecard itself will have the values so maybe this graphic is fine just as it is when used in conjunction with the other devices.
