“The FORCAST formula is very unusual in that it does not use a sentence-length measurement. This makes it a favorite, however, for use with short statements and the text in Web sites, applications, and forms,” writes readability expert William DuBay in Smart Language. He vouches for its accuracy from the 5th to the 12th grade.
FORCAST = 20 – (M/10). M is the number of monosyllables in a sample of 150 words. Fascinated by the formula’s simplicity, I wrote about it in ‘Fascinating Approaches To Readability’. However, if I may be allowed to cavil, the minus sign is a bit of a problem as it is more difficult to subtract than to add. How nice it would be if there was a plus instead!
I found an easy way to eliminate the minus sign. By a simple substitution process, I arrived at a formula with the plus sign. In a sample of 150 words, there are monosyllables (M) and non-monosyllables (N). These are mutually exclusive categories, yielding the equation M + N = 150. So, M = 150 – N. Now, FORCAST = 20 – (M/10) = 20 – [(150 – N)/10]. On simplification, we find that the minus sign disappears. And the new formula FORCAST Plus = (N/10) + 5.
Text difficulty increases as the number of non-monosyllables increases. One can easily guess, while choosing a sample of 150 words, whether the text has more monosyllables or non-monosyllables. One can also guess whether a text is meant for the lower or the higher grades. To subtract or to add: that is the question.
The FORCAST and the FORCAST Plus yield the same answers. Up to grade 12, non-monosyllables in a text are fewer than monosyllables; and so N is easier to count than M. But from grade 13 onwards, monosyllables are fewer than non-monosyllables; and so M is easier to count than N. If you count M, you will have to subtract something from 20. If you count N, you just have to add something to 5. To subtract or to add: that is the question. Since DuBay vouches for the formula’s accuracy from the 5th to the 12th grade, I recommend FORCAST Plus.