From the Department of Potentially Misleading Facts and Figures

So everyone is blogging about this chart, which was pulled together by AEI’s Andrew Biggs:


The potential significance of these data for any number of common understandings of the factors behind rising medical costs is immediate, but – and speaking as a statistical ignoramus, so pillar of salt and all that – the way that they’re being presented here is doing some pretty significant work, isn’t it? Crucially, it seems clear to me that the numbers should at least be calculated in terms of per capita expenditures, since as it stands we aren’t shown how much of the total growth in each case is due to simple increases in human and non-human animal populations. And based on what I could glean from a quick search, the U.S. pet population increased by about 17% from 2001 to 2007 alone, which would give an annual growth rate of almost 3% in contrast to a U.S. population growth rate of about a third of that. Biggs’s graph (I couldn’t figure out how to dig his original data out from the Consumer Expenditure Survey) does suggest an increase in veterinary expenditures more on the order of 30% or so during that same stretch, so it’s clearly not as if there hasn’t been a notable increase in veterinary expenditures per pet, but not accounting for this sort of complicating factor seems a significant omission, no?

I’m sure a better number-cruncher than I could use this as an inspiration to put a more revealing chart together – get to work, Conor Clarke! – but in any case the data were interesting enough that I thought it worth pressing on them a bit.