Louis Leon Thurstone (1887–1955)
Louis Leon Thurstone was an American psychologist and statistician, a pioneer in psychometrics and the measurement of human abilities. He is best known for his work on factor analysis and his multi-factor theory of intelligence.
In 1919, Thurstone published The Learning Curve Equation, a careful study of how a group of 51 student typists improved with practice. Over several weeks he administered four-minute typing tests and recorded the average words-per-minute score at each successive stage. He found that the data followed a rational function:
Y = 216(X + 19) / (X + 148)
where X is the total number of pages of practice written, and Y is the average words-per-minute score in a four-minute test. The value 216 is the predicted upper limit — the speed a typist would approach but never quite reach. Thurstone called this the "practice limit."
The curve starts around 28 words per minute (for a student who has written no pages at all) and rises steeply at first, then flattens as the practice limit is approached. The shape is familiar from many domains: early gains come quickly; later gains require disproportionately more work.
This game
This game gives you four minutes to copy a passage. Your word count is scored with a lookahead rule that allows skipping up to two reference words — a misspelled or skipped word does not stop the counter, but it also does not add to it. The server is the final authority on your score.
Your score Y is inverted through Thurstone's formula to find the equivalent X — the number of pages a typist in the 1919 cohort would have needed to write to reach your speed. A score below the Y-intercept (≈ 28 words) places you "below the floor" — exactly where every one of Thurstone's students started, before they had written a single page.
Credits
Created by César A. Hidalgo. The typing passages are drawn from his books Why Information Grows and The Infinite Alphabet (available here).
Source: Thurstone, L. L. (1919). The learning curve equation. Psychological Monographs, 26(3), 1–51.