READING RATES 



501 



4.5 



16 32 64 



VOCABULARY SIZE 



128 



256 



5000 



WORD 



DICTIONARY 



Fig. 2 — Reading rate is essentially independent of vocabulary sizes under 

 certain conditions. 



must make each of these factors large. As Fig. 3 indicates, reading speed 

 tends to decrease as vocabulary size increases. From the data in Fig. 3, 

 a rationale (shown in Appendix I) was developed for use in searching 

 for an improved vocabulary which would maximize transmission rate. 

 This indicated that the 2,500 most familiar monosyllables chosen with 

 equal probability should form a very good vocabulary and one which is 

 simple to construct and use. For a 2,500-word list we have 11.3 bits/ 

 word. 



Reading speeds for such preferred lists were 3.7, 3.4 and 3.0 words/sec, 

 giving information transmission rates of 42, 39 and 34 bits/sec. Some 

 data on the distribution of this rate found among Bell Telephone Lab- 

 oratories employees is given in Fig. 5. 



Experiment 4- Prose and Scrambled Prose 



The experiments above were all with discrete Avords. Reading rates 

 for non-technical prose* are appreciably higher — 4.8, 4.7 and 3.9 

 words/sec for the three readers. However, such prose has a good deal 

 of redundancy. Shannon" arrives at a figure of around 1 bit/ letter for a 



* Extracts were taken from Xew York Herald Tribune, the novel "East River" 

 by Sholem Asch, "Vermont Tradition" by Dorothj' Canfield Fisher and the 

 Scientific American. Such material was chosen as being of the same sort of prose 

 as was used by Dewey* in his word counts from which Shannon" made his estimate 

 of information content of printed English. 



