Wednesday, January 22, 2014

Displaying Ordinal Data (Bidirectional)

The following stacked bar graph has many advantage:

  • The most intense ratings are stacked nearest the axis, with decreasing intensity away from the axis.  Hence the top of any bar corresponds to the % of subjects with at least that intense of a response.  
  • E.G.: at a glance: For the EOS group A observation, about 10% scored "Very Much Improved" (top of the dark green), while 30% scored at least Much Improvement (top of the light green), and 30% any improvement (NB: no one scored "Minimally Improved")
  • The above axis item correspond to improvement, and below axis items correspond to worsening
  • E.G.: In the Day 28 Group A observation, few scored Very Much Improvement or Worsening, and about equal numbers scored improvement as worsening. 
  • Ratings of "No Change" are implied, but not shown.
  • E.G.:  For Day 28 Group A, about 30% improved, 40% worsened, leaving 30% with no change.

Generic Description (for Statistical Analysis Plan)
For birectional ordinal data (such as CGI-I), the same concept as for unidirectional ordinal data is used but with desirable scores (e.g., improvement) plotted above the horizontal axis, and undesirable scores (e.g. worsening) plotted below the horizontal axis. For either category, the most extreme ratings will be closest to the horizontal axis, and assigned the most intense colors. This will allow an immediate visual impression of the relative proportions of patients who improved versus those who worsened, and by how much.

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