Chen (1) has formulated a number of indices and ratios which are useful in determining the course of development of pre-meaningful speech. He has also formulated a differential speech development index based upon the difference between speech sounds considered as isolated elements at a given infant age level and the status of these elements in adult speech. The adult speech standard used for comparison is that by Voelker (3). There are two forms of this index described, elsewhere (2). One is the difference between the number of speech sounds elements in infants and adult speech, the second form is the differential percentage index based on the difference in the percent of frequencies in the use of vowel and consonants of infants and adults. A group of infants under 30 months were used. Intelligence test scores were secured by means of the Kuhlmann Test of Mental Development
