Department of Awful Statistics: Why Ask Y?

By Megan McArdle

It is that time of year again: the time when advocacy groups produce graphs with Y-axes that start at some arbitrary number in order to make their issue look bigger.  Consider this heart-rending graph from the Working Poor Families Project (via Felix Salmon):


working.jpg

Why does the graph bottom out at 25, you may ask.  Why indeed? This is what it looks like when it starts at the more traditional number of zero:


Working Families2.png

It looks like the percentage actually doesn't change that much, moving up slightly in recessions, and down slightly in good times.  We see that now, in a remarkably deep recession, it gets a little worse.  But not surprisingly so.  In the top graph, the changes look approximately five times bigger than they are.


This is not to downplay the problems of poverty and near-poverty, which are a discussion for another day (but for which I'm not sure 200% of the poverty line is a particularly useful measure).  It's simply to point out that things can look very different depending on where you start the Y axis.  And in my experience, as advocacy groups launch into their end-of-year fundraising season, Y axes seem to creep closer and closer to the bottom value in the series.

This article available online at:

http://www.theatlantic.com/business/archive/2010/12/department-of-awful-statistics-why-ask-y/68359/