Clearing the Air of Fog and Smog

The purpose of a readability formula is to produce a number or number range which approximates the achievement level required of a reader in order to comprehend a written passage. A useful formula, especially to the classroom teacher, is one which is easily computed and which accurately predicts the needed reading ability. Two formulas which have appeared in recent years, the Fog Index and the SMOG Grade, are easily applied. But are they accurate