Word Frequency

In addition to being an index of concept frequency, word frequency could be an index of difficulty, as well (Ryder & Hugues, 1985). Word frequency, together with students’ word knowledge, could be a significant predictor of word and text

readability (Lin & Hu, 2002). Besides, Lotto & DeGroot’s (1998) study manifested that high-frequency words are easier to learn and retrieve than low-frequency words.

(1) Commonness and Familiarity

A consensus has been reached that vocabulary frequency lists play an important role in curriculum design, setting learning goals, vocabulary assessment, and textbook evaluation (Nation & Waring, 1997; Read, 2000). The frequency of a word indicates its occurrence across a wide range of texts. The higher frequency a word has, the earlier it should be taught or learned (Coady, et al., 1993, Nation & Waring, 1997). On the other hand, Freebody and Anderson (1983) claimed that low-frequency words in a text could produce a negative effect on comprehension based on the results of their experiment showing that one low-frequency word in six running words caused decrease in comprehension.

If so, how frequent should a word appear to be categorized as a high-frequent word? In accordance with Nation’s (2001) analysis, “usually the 2000-word level has been set as the most suitable limit for high-frequency words (p. 14)” since it covers about 80% coverage of texts. Nation adopted Michael West’s General Service List as the list of high-frequency words. Moreover, Nation also promoted the learning of Academic Word List (Coxhead, 2000), particularly for EAP (namely, English for Academic Purposes). The list consists of 570 word families that are not in the most frequent 2000 words of English but which occur reasonably frequently

over a very wide range of academic texts. Nation does not recommend learners to learn the third 1000 words but Academic Word List because the former only offers 4.3% extra coverage while the latter provides additional 10% coverage.

(2) Repetitions or Exposures

Word frequency, which not only could illustrate the commonness and familiarity of a word but also represents the exposures sufficient for successful learning, also affects vocabulary learnability. Using Stevick’s (1982, p.30) term, the “intensity” of encounters with a word has significant effects on the increase and retention of world knowledge. No instruction of strategies, such as guessing word meaning in the contexts or incidental learning, guarantee the acquisition of a word at the first encounter with the word or with only one exposure to it. Without multiple exposures or repeated encounters may a word and its related knowledge reach in a learner’s long-term memory and then his or her lexicon (Nagy, 1997; Nagy, Anderson, &

Herman, 1987; Rubin, 1992). Concerning the incidental learning process during reading, several studies also urged that only repeated exposures through extensive reading would lead to integration of new words into the learners’ second language lexicon (Day, Omura, & Hiramatsu, 1991; Dupuy & Krashan, 1993; Pitts, White, &

Krashen, 1989).

In the study conducted by Nagy, Herman, and Anderson (1985), word occurring only once in the text when answering a multiple-choice question on word meaning, their subjects had merely as low as 5% probability of correctness. In order to examine the vocabulary burden for students by means of word-frequency counts, Cheung (1986) investigated English vocabulary in the 36 junior and secondary textbooks in Hong Kong. He argued that if a word occurred only once in the word list of a certain class level, it should not receive any attention and nor did low frequency words deserve much attention. Another research done by Hulstijn et al. (1996), who

controlled the variable of exposure frequency, illustrated that although learners more readily recognized words they had encountered three times during reading than those they had encountered only once, they often were not able to infer the correct meaning of any words of the three encounters.

If one exposure is too few to gain attention and three encounters are still not enough, how many times should a word which is not taught with specific attention to be repeated in order to be learned? Some studies suggested a range of 5-16 encounters with a word for a learner to truly acquire it (Crothers & Suppes, 1967; McKeown et al., 1985). Saragi, Nation, and Meister (1978) found that words presented fewer than six times where learned by half of their subjects, while words presented six times or more were learned by 93%, suggesting a threshold of six encounters. The findings were echoed by Rott (1999), who also located six encounters as the watershed. Horst, Cobb and Meara (1998) regarded that words encountered eight times or more were able to have a good chance of being learned incidentally.

Learners of different levels in different surroundings should need different numbers of encounters. Horst, Cobb and Meara (1998) investigated the relationship between exposure frequency and proficiency level of EFL learners. Their study presented that learners who knew more words needed fewer encounters to learn another word, while learners who knew fewer words required more encounters.

Focusing on Taiwanese EFL learners, Liu (2002) discovered that the optimal pick-up exposure frequency range for EFL senior high students with different English

proficiency fell at the range from six to twelve exposures.

Based on the theories of human memory, when a word is recalled, the learner would evaluate it subconsciously, and then could decide how it is different from others and go on to change his or her interpretation until he or she could reach the exact meaning that fits the context (Baddeley, 1987). The findings of a number of

relevant studies discussed above have clearly illustrated the significant effects of multiple repetitions and exposures on the increase and retention of word knowledge.