In addition to everything everyone else has said: their math is off by half (or 100%, depending on how you count), due to a structural error.
(context: native English speaker, big reader, huge nerd, perfect SAT score)
I got all 100 correct on the first try without looking anything up! Confusingly, that only resulted in a "SCIENTIFIC ESTIMATE" that I know 85,000/~170,000 words?
Their "How is this calculated" page that appears at the end explains their error:
> According to the Oxford English Dictionary (Second Edition), there are approximately 171,476 words in current use.
> We use Stratified Sampling. Instead of testing random words, we divide the language into 5 distinct difficulty bands based on frequency of use:
> 1. Core Basics ~3,000 words
> 2. Intermediate ~7,000 words
> 3. Advanced ~10,000 words
> 4. Expert ~25,000 words
> 5. The Obscure ~40,000+ words
> If you answer 2 out of 3 'Intermediate' questions correctly, we estimate you know roughly 66% of the 7,000 words in that band.
> Total Score = Σ (Accuracy in Band × Band Size)
Their strata add up to 85000, not ~170k, making a perfect score still give a 50%.
They're also using a pretty limited and perhaps non-difficulty-representative subset of the language.
Cute, but wrong on many counts.
(context: native English speaker, big reader, huge nerd, perfect SAT score)
I got all 100 correct on the first try without looking anything up! Confusingly, that only resulted in a "SCIENTIFIC ESTIMATE" that I know 85,000/~170,000 words?
Their "How is this calculated" page that appears at the end explains their error:
> According to the Oxford English Dictionary (Second Edition), there are approximately 171,476 words in current use.
> We use Stratified Sampling. Instead of testing random words, we divide the language into 5 distinct difficulty bands based on frequency of use:
> 1. Core Basics ~3,000 words > 2. Intermediate ~7,000 words > 3. Advanced ~10,000 words > 4. Expert ~25,000 words > 5. The Obscure ~40,000+ words
> If you answer 2 out of 3 'Intermediate' questions correctly, we estimate you know roughly 66% of the 7,000 words in that band.
> Total Score = Σ (Accuracy in Band × Band Size)
Their strata add up to 85000, not ~170k, making a perfect score still give a 50%.
They're also using a pretty limited and perhaps non-difficulty-representative subset of the language.
Cute, but wrong on many counts.