Perhaps the rising vocabs are due to more education, or both are due to increasing...something: A reader suggested as a straightforward explanation that whites and especially blacks are doing better on the GSS vocabulary test because they are staying in school longer. I calculated the mean years of schooling for both races for each of the past four decades to see if the pattern matches the vocab trends. They look to me like they do. Take a look:
Blacks--mean years of schooling
Whites--mean years of schooling
With vocab, we saw a steady improvement among blacks. We see that here too, although the rate of increase in education shrinks over time. With whites, they only saw improvements in knowledge of words between the 80s and 90s. Like blacks, their educational levels have improved every decade since the early 70s, but the biggest increase was between the 80s and 90s, the same span of time that they developed better vocabs.
In the past 3 or 4 decades, many more Americans are getting at least some college experience, and college is a place where many people hear words they rarely hear any place else--the very words that are likely to show up on a vocab test. This is especially true of blacks.
Or, something deeper is going on which has raised educational and word knowledge levels together? Have people gotten smarter, hungrier for learning because of better nutrition perhaps? This sounds more plausible if we're talking about the beginning of the century, not the end of it. Perhaps the growth of the "information society", which pushes people to stay in school and exposes them to more novel words? What do you think?