Frequency of word usage and perceived word difficulty ratings of kuvcera and francis words

Twenty-four judges estimated the conceptual difficulty level of 870 five-letter words, using a 5-point scale. The words were selected from three word-frequency categories (1, 5–10, and 50–3,562/million) based on the word counts provided by Ku{\v{c}}era and Francis (1967). The ratings were reliable. Tables in this paper list the means and standard deviations of the ratings for each word. Reaction time (RT) for valid word identification was tested in 20 subjects, using four sets of 50 words designed to test the effects of word frequency and word difficulty. RT was longer for more difficult words when word frequency was held constant. A word-frequency effect on RT was present when difficulty was held constant. The relationship of the results to subjective estimates of word familiarity is discussed.