Vocabulary Mastery, Grammar Mastery, Reading Skills, Expository
Texts.
This research aims to examine the effects of Vocabulary Mastery and Grammar
Mastery on Students’ Skills in Reading Expository Texts, both simultaneously and
partially. This study employed a quantitative survey method. The population
consisted of tenth-grade students at state senior high schools in East Jakarta, with a
total sample of 85 students selected through simple random sampling. The data
were collected using vocabulary tests to measure Vocabulary Mastery, grammar
tests to measure Grammar Mastery, and reading tests to measure Students’ Skills in
Reading Expository Texts. The data were analyzed using multiple linear regression
analysis.
The results of the statistical analysis show that Vocabulary Mastery and Grammar
Mastery simultaneously have a significant effect on Students’ Skills in Reading
Expository Texts. This is evidenced by a significance value of Sig. = 0.000 < 0.05,
an obtained F value of 33.734, a multiple correlation coefficient of R = 0.672, and
a coefficient of determination of R² = 0.451, indicating that 45.1% of students’ skills
in reading expository texts are influenced jointly by Vocabulary Mastery and
Grammar Mastery. Furthermore, Vocabulary Mastery has a significant effect on
Students’ Skills in Reading Expository Texts, as indicated by a significance value
of Sig. = 0.005 < 0.05 and a t value of 2.858, with a contribution of 20.66%.
Grammar Mastery also has a significant effect on Students’ Skills in Reading
Expository Texts, as shown by a significance value of Sig. = 0.001 < 0.05 and a t
value of 3.298, contributing 24.44%, which is higher than the contribution of
Vocabulary Mastery. These findings indicate that Grammar Mastery has a stronger
influence on students’ reading skills in expository texts compared to Vocabulary
Mastery.