Most readability metrics use some combination of the average number of words per sentence and the average number of syllables per word (the latter being a crude metric of word rarity), though some compare against a whitelist of common words similar to (but usually larger than) the one XKCD’s using. If people feel a need to use enough circumlocution to make up for removing rare words, the gains in the latter might not outweigh the losses in the former.
The details vary quite a bit by formula. I tried several readability analyses on portions of this post vs. an Up-Goer 5 compliant version, and found that while the compliant version was consistently scored lower, the deltas varied from almost nothing to several grade levels.
(As an aside, plugging stuff into the Up-Goer 5 Text Editor kind of reminds me of Mad Ape Den. Not quite as restrictive, though.)
Most readability metrics use some combination of the average number of words per sentence and the average number of syllables per word (the latter being a crude metric of word rarity), though some compare against a whitelist of common words similar to (but usually larger than) the one XKCD’s using. If people feel a need to use enough circumlocution to make up for removing rare words, the gains in the latter might not outweigh the losses in the former.
The details vary quite a bit by formula. I tried several readability analyses on portions of this post vs. an Up-Goer 5 compliant version, and found that while the compliant version was consistently scored lower, the deltas varied from almost nothing to several grade levels.
(As an aside, plugging stuff into the Up-Goer 5 Text Editor kind of reminds me of Mad Ape Den. Not quite as restrictive, though.)