Date of Award

Fall 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

April Ginther

Committee Chair

April Ginther

Committee Member 1

Tony Silva

Committee Member 2

Margie S. Berns

Committee Member 3

Dwight Atkinson


Lexical proficiency is strongly correlated with L2 productive language ability (Crossley, Salsbury, & McNamara, 2011; Laufer & Nation, 1995). While many studies have investigated the relationship between lexical proficiency and L2 writing ability, not many studies have been conducted in terms of spoken language. Also, few studies have focused on how non-native English speakers with different L1 backgrounds differently or similarly develop lexical proficiency in L2 speaking. Based on this background, the present study is conducted with three purposes: 1) to compare the effectiveness of measures of lexical proficiency in terms of their ability to predict the quality of L2 spoken production, as determined by scores on the Oral English Proficiency Test (OEPT) at Purdue University; 2) to compare the different lexical features among different levels of L2 oral proficiency; 3) to see whether different L1 backgrounds present different levels of development of lexical proficiency. ^ A quantitative research approach was selected in this study. Three hundred and three speech samples from the Oral English Proficiency Test (OEPT), representing four different L1 groups of Korean, Mandarin, Hindi, and English, were collected, and in order to measure lexical proficiency, the Lexical Frequency Profile (LFP) was employed. Statistical inferences were based on Spearman rank order correlation coefficients and descriptive statistics.^ Results showed that OEPT scores have strong or moderately strong correlations with some indices of lexical proficiency. Interestingly, however, different results were obtained when the Spearman rank-order correlation coefficients were rerun without Mandarin groups: the correlation coefficients increased for the variables with Types, TTR, D, K1 Type, K2 Type, AWL Type, and Off Type. Descriptive statistics suggested some reasons for the different results with and without the Mandarin group: basically, the Mandarin group created more lexical diversity and produced more words as compared to other sub groups than the Korean or Hindi groups did. Also, the Mandarin group created dissimilar trends in each LFP variable, unlike the Korean and Hindi groups. Also, descriptive statistics on the LFP indicate that L2 advanced speakers express their ideas employing frequent words as a rule rather than infrequent ones. This result indicates that when it comes to vocabulary learning for oral proficiency, frequent words should be a more important focus in L2 vocabulary learning than infrequent words. Each of these results is explored in detail in the Discussion section. Pedagogical implications and suggestions for future studies are discussed as well.

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