Reading Graphs
There’s a blog, Political Calculations, which is immensely satisfying to a highly political data junkie such as myself. So it’s a good blog, but the proprietor really hoses his interpretation of this graph:
[government spending] has literally “gone vertical” during the last two years.
In mathematical terms, that’s the sort of thing you see when you divide any number by zero. Applied to the chart above, that means that the relationship between the change in total government spending and the typical income earned by an American household from year-to-year is now “undefined.”
The problem is that this is a bivariate graph, and the concept of slope in terms of dy over dx does not apply. More precisely, it has little meaning, and manifestly … Continue reading