Narrative charts, like this one shown on the right, are particularly difficult to master. The temptation is strong on the part of the designer to mislead by inclusion/exclusion and on the part of the reader to misjudge by reading between the lines.
The accompanying article made the point that James Frey's fraudulent memoir experienced a severe drop in sales since Oprah "sacrificed" him. Unfortunately, what the chart shows is how choppy sales have been for this book. It experienced a similar drop after his first appearance on Oprah.
In fact, this chart raised a host of unanswered questions:
- How to explain the end-of-year rise in sales back to post-first-Oprah-appearance level?
- What is the purpose of the red line? Is it fair to compare a hardcover with a paperback?
- How to explain the "turbulence" of Frey's memoir sales even before the scandal broke? Why is it that his other book has a much smoother sales trend? (Is it merely a scale effect hiding its ups and downs?)
- Oprah's influence appeared to be highly specific to the recommended book and time of the show. There seemed to be zero impact on the sales of other books by the same author (scale effect?) and a rapidly diminishing impact even for the highlighted book. Is this a general phenomenon?
This type of time-series chart does not provide direct evidence of cause and effect; however, they are commonly used in the media for that dubious purpose. At the best, we can conclude that those factors are correlated, prompting hypotheses and further analyses.
Reference: "James Frey's Falsehoods Improved His Tale", New York Times, Feb 1 2006.