‘A Formula for Predicting the Comprehension Level of Material to be Presented Orally’ by John R. Rogersappeared in The Journal of Education Research (Volume 56, Number 4, December 1962).Rogers developed criterion passages based on the assumption that children understood their own language and that of children in the same age group. He writes: “Four hundred and eighty recordings of more than a hundred words each were used in developing the criterion. An exact typed reproduction of each recording was made. In effect, these transcriptions represented twelve bodies of material — one for each of the twelve school grades.”
The regression equation (0.669x + 0.4981y – 2.0625) is based on two independent variables: 1. Average idea unit length (x), obtained by the number of words divided by the number of independent clauses; and 2. Percentage of words in the sample that do not appear on Dale’s long list of 3000 familiar words (y).Rogerssays that the grade level predicted by his formula ‘would be accurate within a range of about two grades above or below the predicted one more than two-thirds of the time’.
Since the formula appears complex with its decimal points, I have found a useful approximation by choosing a sample of 50 words. If I is the number of independent clauses in the sample of 50 words; and if ND is the number of words not in the Dale list of 3000 words, then GL (grade level) = (33/I) + ND – 2. This formula grades oral texts on a scale of 1 to 12+.
The Dale list was revised in 1983. It is found in Readability Revisited: The New Dale-Chall Readability Formula by Jeanne S. Chall and Edgar Dale (1995). The earlier list may be easily found online. I think that theRogers’ listening formula should work well with either list.
However, a word of caution. Rogers writes: “From the nature of the procedure followed in deriving the formula, it is obvious that the last word has not been spoken. Furthermore, the formula is presented as untried, untested, and unproved. At present there is no graded body of material against which it may be tested. Perhaps other researchers will work out methods for testing the formula in practical situations.”