The Guardian has an interesting chart up, showing the decline of state of the union addresses as measured by the Flesch-Kincaid readability test. See here. Or perhaps it shows the improvement of presidents’ ability to speak intelligibly …
Does anyone know how the Flesch-Kincaid test works? In particular, might older texts rate as more difficult merely because they are older? If so, the downward slope on the chart could be explained easily enough and it might not be so interesting after all. But I don’t know enough about the test to know if it is susceptible to that sort of effect.