## Read That Graph Carefully II

Three years ago I wrote a short piece on how the FT had misrepresented the ratings of President Obama by using an inappropriate vertical scale on a graph it was showing: note that piece was on another of my blogs!

My simple suggestion was to elongate the vertical scale and reinterpret the graph.

I just reviewed that posting and feel I ought to have suggested that we calculate rates of change values for the ratings rather than just change the chart. That will give us a complete picture.

Here’s the original graph:

Here is my table of data: assumed values from the chart then calculated values of the rates of change. Finally my own graph showing both sets of numbers: look at the impact of the rates of change values!

 Year Month Change % Rate of Change % 2009 Feb 66% 2009 Mar 63% -4.55% 2009 Apr 61% -3.17% 2009 May 64% 4.92% 2009 Jun 64% -0.78% 2009 Jul 60% -5.51% 2009 Aug 55% -8.33% 2009 Sep 52% -5.45% 2009 Oct 52% 0.00% 2009 Nov 52% 0.00% 2009 Dec 50% -3.85% 2010 Jan 51% 2.00%

Sorry the example is so old but it’s a good one because the rates of change are at such apparent odds with the way the chart was originally presented.

Duncan Williamson

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