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  • Kyaw Moe Aung thinks this is interesting:

Automated readability index is a measure of the text complexity and a reader's ability to understand. A specific formula is used to calculate this index: 4.71(# of characters / #of words) + 0.5(# of words / # of sentences) – 21.43.

From

Cover of Mastering Machine Learning with R

Note

Automated readability index - measurement of complexity.