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This, according to Dan Goldstein, who found the following chart:
For bar charts, one must start at zero... no exceptions. Chopping off arbitrary amounts of the base can create different perceptions of difference.
Here is another example.
Posted on Jul 06, 2011 at 12:25 AM | Permalink
Fabulous! Looks like 328 is about 25% larger than 327! I did not know that.
Jul 07, 2011 at 08:41 AM
I think the link is suppose to be http://www.decisionsciencenews.com/2011/07/03/best-graph-ever/
Dan Goldstein |
Jul 08, 2011 at 10:46 AM
First of all, congratulations on finding such an amazing stream of terrible charts as cautionary tales. This bar chart is inexcusable and the title of the post is perfect!
I am not sure I agree with your absolute admonition that "For bar charts, one must start at zero... no exceptions." I would agree that this is something that should only be done for a good reason, but I am not sure about never...
Would you never plot temperatures (or other interval scale variables) on a bar chart? How about on a line chart? Or would you always include the 0 Kelvin baseline?
What if you were comparing variables with a non-zero lower bound (say SAT scores across school districts or credit scores of mortgage applicants over time).
What about variables with fuzzy lower bounds - say IQ scores or cholesterol levels? Say you wanted to compare cholesterol levels across ethnic groups? Or test whether the IQ of military recruits went down as the military strained under the weight of two wars? What if you know that the military has an 85IQ point minimum requirement?
Jul 11, 2011 at 02:26 PM
My graphic design friend was once tasked with a graphic that was to include a bar chart. He asked me to critique it, and the first thing I told him was "you need to use a proper scale for your bar chart". He didn't start the scale at some non-zero number - he just used arbitrary lengths for the bars. The order was correct, but he really didn't even make an effort to get the lengths right - because it honestly didn't occur to him that he should have.
This may not be too common, but it does happen.
Jul 12, 2011 at 02:14 PM
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