Rudolph Flesch is famous for his Plain English campaign. Yet his name is associated with readability formulae that are far from plain. If AWS is the average words per sentence; and ASW, the average syllables per word —
* FRE (Flesch Reading Ease) = 206.835 – 1.015AWS – 84.6ASW
* FKI (Flesch-Kincaid Index) = 0.39AWS + 11.8ASW – 15.59.
The FRE scale ranges from 1 to 100: higher the score, simpler the text. A text that tests 90 and above is suitable for the fifth grade. The FKI is an attempt to grade the FRE on a scale of 1 to 17. In this scale, the score indicates the grade-level of the text: the higher the score, the more difficult the text. For example, a score of 11 indicates that the text is suitable for the 11th grade.
These formulae, with its decimal points, intimidate writers rather than compel them to test their writing with a formula. Though Davis Foulger made a successful attempt to simplify the counting procedure, his ‘A Simplified Flesch Reading Ease Formula’ is equally complex. His article is available online at http://foulger.info/davis/papers/SimplifiedFleschReadingEaseFormula.htm
My argument is that any formula for Plain English must be plain, simple and beautiful. Without mincing words, I present that simplification:
SFG (Simple Flesch Grading) = (AWS/10) + 10(ASW – 1)
For grade-conversion, I used the formula 13 x [1 – (FRE/100)] + 4. The actual result ran into several decimals and looked complicated. But I found that an approximation looked simple and compelling. And I called it Simple Flesch Grading. But how reliable is the SFG?
Instead of testing the formula on actual texts, I substituted possible values for the variables AWS (5, 10, 15, 20, 25, 30, 35, 40) and ASW (1, 1.5, 2, 2.5, 3, 3.5, 4). I do understand that all these combinations are not equally likely. I have tabulated the results for FRE, FKI and SFG. Please take a look at the table at http://www.angelfire.com/nd/nirmaldasan/readability/sfgtable.htm
The relationship between these formulae is shown by the Pearson’s product-moment correlation: – 0.927942 (FRE and FKI); – 0.98567 (FRE and SFG); 0.90755 (FKI and SFG). The correlation indicates that SFG is a reliable indicator of readability.