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New results for native speakers

25 July 2011

Over the past week, we've had a flood of participation, with over 200,000 visitors. (If you haven't taken the quiz, you can do it here.) So now it's about time we gave something back! Previously, we'd only been able to calculate a very narrow range of statistics.

But now, we've been able to produce two great new charts which give a much fuller picture of the vocabulary sizes of native English speakers. First, since we've had much more participation from both younger and older speakers, we can calculate meaningful average vocabulary sizes from native English speakers who took the test, for ages 3–71:

This is a fantastic chart, because it shows the speed at which our vocabulary really grows. Between the ages of 3 and roughly 16, our vocabulary explodes at an average rate of almost 4 new words a day (3.8, to be more exact). Then, between the ages of 16 and 50, our vocabulary growth is slower, but still fairly consistent: around 1 new word a day (0.85, to be precise). Finally, beyond 50, vocabulary size appears to remain fairly constant. (Note that the data is still a bit jagged both for younger and older participants — we still need more data at both ends to smooth things out.)

However, note that these average vocabulary sizes of our respondents are significantly higher than those of the overall population at large. How do we know this? Because our American participants' self-reported verbal SAT scores hover at around a constant 700 (out of 800 maximum) at all applicable age levels, while the median score of SAT test-takers is only 500. And these test-takers themselves are a more educated subset of the American population as a whole. To put things in perspective, it has been estimated that if the whole US population took the verbal SAT, it would have a median verbal score of around 350. Our average respondent's verbal SAT score of 700 places him or her in the 95th percentile among SAT takers, and above the 99th percentile in the American population as a whole. This means that the average American's vocabulary size would be significantly lower than the chart above shows.

But with the new data we've acquired, we've been able to produce a second chart, more limited in age range, but which shows the levels of vocabulary growth among respondents of different verbal SAT scores:

Note: V-SAT scores are as reported, and have not been adjusted to account for the 1995 test re-centering.

First, this appears to tell us that the verbal SAT really is measuring something real, which is always good to know! But more interestingly, the data so far suggests that vocabulary growth over the years is independent of SAT score—all the slopes are essentially the same, with everyone learning the same "one new word a day" of vocabulary growth. It also shows that, at least in this SAT range of 500–800, each 50-point increase in score is equivalent to knowing roughly 1,500 more words, regardless of your age. The difference between a 500-scoring adult and an 800-scoring adult is roughly an extra 10,000 words in their vocabulary.

You may notice that, while the top-scoring lines are smooth and don't touch (because we've got lots of data), the lower-scoring lines become increasingly jumpy. This is because we still need more participation at these SAT levels — in fact, we don't have enough data to draw any reliable lines for SAT scores under 500. So, we're still waiting for more participation in order to calculate the lifetime vocabulary curve of an "average" American, with a verbal SAT score of 350.