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Fun With the Y Axis

By Matthew Yglesias  

"Fun With the Y Axis"

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This suggestive chart from Andrew Biggs at AEI seems to have impressed Greg Mankiw. It shows, allegedly, that the growth in health care spending has tracked the growth in veterinary spending:

vetspending2-1

But look at the Y axes. They don’t match up! This is almost a chart in which the same vertical distance that denotes a $2 billion increase in veterinary expenditures represents a $500 billion increase in human health care expenditures. But not quite. Note that the distance between $2,000 billion and $2,500 billion on the right axis is clearly larger than the distance between $10 billion and $12 billion on the left.

I’m not sure what difference cleaning the charts up would make, but it would certainly make them a lot easier to interpret. One would also want to do some kind of normalizing by population size. Has the number of pets grown relative to the number of people? Shrunk? We know that the demographics of the human population has been aging, but probably not the pet population.

Update

Apologies . . . as you can read in the comments I’ve got this wrong. The chart is correctly scaled, and a correctly scaled chart just doesn’t happen to involve nice round numbers lining up. The data does, in fact, show exactly what the chart purports to show namely that the growth rate of veterinary spending is basically the same as the growth rate of spending on human health care.

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