Wednesday, October 28, 2009

Some more graphical design

So, I came by yet another bad chart here. Check out the graph below, which was used in a presentation:

First of all, it suffers from of number of graphical flaws of more or less importance:
  • Vertically aligned text (the years)
  • The use of color (too much)
  • The grey back ground and the ultrabold lines around the legende.
  • The wrong chart type used.
But above all, there is one really major flaw which is unforgiving: It misrepresent the data.
I didn't relised this before I started plotting my own version of this chart. But the stacked bar chart is to represent part to whole ratio. The way it's supposed to be used in this case, is that the whole bar shows the total number of days. The strong color is emergency(ØH) and the lighter color is the planned days (Elektive). I thought it was strange that the emergency days were so much more then the planned days, and when I check the numbers, I found out it wasn't so. The planned days is actually the whole bar, i.e. the sum of the dark and light colored areas. Totally wrong representation of the data.

Also, I do believe that the point of the chart is to show trends over time. That is something a line chart does much better then a bar chart. My version represented the data truely in a line plot, and I also adjusted the colors to look more professional:

I chose to start the y-axis at 2500 rather then 0 (which you can do in a line chart, but not in a bar chart) to expand the data as much as possible in the y-direction to show the variation as clearly as possible. Didn't gain much, so it's better to start at 0 if the relationship between planned and emergency days are important. I also added light grey lines to show the quarters, as these kind of data usually is collected every third month.

If the total numbers of days are important, I would represent this in a three panel chart. Every chart has the same range on the y-axis, but different starting point:

Of course, if the relationship between emergency and planned days is important, a fourth panel of the ration could be added. Or replace the total panel.

(PS: I just noticed I forgot to add the correct weight to the line on the x-axis, but I'm too lazy to correct it)

Edit: I did notice that my source for the numbers was wrong. So the actual numbers may be wrong, but the design of my charts are still valid.


Wilhelm said...

Good call! I see that you also fixed another critical flaw in the figure in that you translated the text from nynorsk to bokmål :-)

Seriously - looking at the first figure in full size is the closest I've ever been to having an epileptic seizure. MAN was that hard on the eyes. Not to mention that you can teach yourself another language in the time required to understand the legend and apply it to the graphic.

Anders said...

To make it even worse, the original graph is a template and is repeated with different parameters through-out the presentation. And this presentation is held at least every third month. God knows who picked those colors and thought they were good...

Wilhelm said...

Brutal inability to remove default Excel grey background.