A standard text aims for a Flesch Reading Ease score ranging from 60 to 70. In ‘A New Readability Yardstick’ of 1948, Rudolf Flesch presents a pattern of Reading Ease scores along with a seven-point scale: very difficult, difficult, fairly difficult, standard, fairly easy, easy and very easy.
In this article, we will look only at the standard text and the averages that go with it. According to Flesch, the average sentence length in words is 17 and the average number of syllables per 100 words is 147. So a typical magazine such as digests will have about 17 words per sentence and 1.47 syllables per word.
In The Art of Plain Talk, Flesch writes: “First, sentence length is measured in words because they are the easiest units to count: you just count everything that is separated by white space on the page. But don’t forget that you might just as well count syllables, which would give you a more exact idea of sentence length: a sentence of twenty one-syllable words would then appear shorter than a sentence of ten one-syllable words and six two-syllable words. Keep that in mind while counting words.”
Since a more exact idea of sentence length is desirable, let us agree to count syllables instead of words. Then the standard text will have about 25 syllables per sentence [17 words per sentence x 1.47 syllables per word = 24.99 syllables per sentence].
The Strain Index, which I derived in 2005, is based on just this one variable: syllables per sentence multiplied by a factor of 0.3. For a standard text, the Strain Index = 0.3 x 25 = 7.5. Thus anyone with about eight years of schooling can understand a standard text.