Petraeus Chart

I can’t decide if this final chart from General Petraeus’s report is the worst ever or the best ever.

Petraeus Recommended Force Reductions Chart

What makes it the worst chart? Mainly the axes.

  • unlabeled Y axis — you have to rely on the text of the report to know the Y axis is brigades.
  • no Y origin — it’s standard for bar charts to start at 0 since their values are encoded as lengths. Here, not only do the bars float, but the axis origin is not even labeled. Is 0 at the base of the bars or at the blue line or elsewhere?
  • nonlinear Y axis — the distance between 15 and 20 is noticeably smaller than the distance from 10 to 15 and from 5 to 10. The distance from the presumed 0 to 5 also very different.
  • irregular Y axis labels — it’s unusual to have labels at 5, 7, and 10 instead of evenly spaced labels such as 5, 7.5, and 10, but at least the 7 is closer to 5 than 10.
  • star images around brigade ranges add useless clutter.

What makes it the best chart? The purpose of a visualization is to communicate a message, and this chart somehow communicates the paradoxical message, “we have a detailed plan, but we just don’t know the details.” The definite bars and dated call-outs show certainty while the fuzzy axes and question marks show uncertainty. So in a sense, the chart communicates its message perfectly.

However, there’s something unsettling about the duplicity of the chart. The normal way of showing uncertainty is with confidence intervals, showing the lower and upper limits with 95% confidence. That’s hard to do with a stacked bar charts like these, so I would split the roles into two kinds, Overwatch and Combat (Partnering and Leading). These two summary roles could be plotted separately each with confidence bands.