Sixty years ago, Rudolph Flesch revised his original readability formula, which predicted difficulty on a scale of 0 (‘very easy’) to 7 (‘very difficult’), and made it ‘a more useful instrument’. In ‘A New Readability Yardstick’, published in the Journal of Applied Psychology (3 June, 1948), he replaced the count of affixes with a count of syllables, expanded the scoring system (100 points) and ‘turned around’ the formula ‘by reversing the signs to predict reading ease’.
The Flesch Reading Ease (FRE), in its general form, is calculated by measuring the average words per sentence (AWS), the average syllables per word (ASW) and substituting their values in the expression 206.835 – (1.015 * AWS) – (84.6 * ASW). Flesch suggests a simple procedure to count the syllables. He writes: “To save time, count all syllables except the first in all words of more than one syllable and add the total to the number of words tested.” However, he did not incorporate this idea of excess syllables in his formula.
Irving Fang’s Easy Listening Formula, measured by the number of syllables more than one per word in a sentence, seems to have been inspired by Flesch’s simple syllable-counting procedure. And, taking a leaf out of Fang’s book, Davis Foulgers incorporated the count of the excess syllables in the Flesch formula. Foulgers’ Simplification (FS) is 122.235 – (1.015 * AWS) – (84.6 * AXW). The new variable AXW is the average number of excess syllables per word. The FS has achieved two things: first, the constant has been reduced from 206.835 to 122.235; and second, syllable-counting has been reduced to the counting of excess syllables. And, what is more, the FS gives the same answers as the FRE.
But one can ask for more! A further simplification is achieved by subtracting FS from 100 and ‘turning around’ the scoring system to predict reading difficulty instead of reading ease. Here follow the Flesch Reading Difficulty (FRD) formula and the ‘turned around’ scoring system:
FRD = (1.015 * AWS) + (84.6 * AXW) – 22.235
Scoring system: 0 to 10 (very easy, 5th grade); 11 to 20 (easy, 6th); 21 to 30 (fairly easy, 7th); 31 to 40 (standard, 8th to 9th); 41 to 50 (fairly difficult, 10th to 12th); 51 to 70 (difficult, 13th to 16th); and 71 to 100 (very difficult, college graduate).
The FRE, the FS and the FRD yield the same answers. Sixty years ago, it was the FRE for calculating reading ease. And now, I think, it will be the FRD for calculating reading difficulty.