The Theoretical Hypothesis of the Study

As a main instrument for this study, test was used to collect data about students‘ score in each group before and after treatment. Such data was needed to find out which group that had significant higher mean score; either it was an experimental group or a control group. This information was obviously needed to determine whether the use of CALL in teaching past tense was effective for students or not. However, before the test was delivered to the sample, such test had to be tested in term of its validity and reliability. The next was interview. Interview was also used in this study as a secondary instrument. It was used to collect data about students‘ opinion equipped with their reasons for answering two questions which were directed to bear a conclusion i.e. whether CALL was effective in teaching past tense or not. The interview was held to 12 students in the experimental class. They were selected by using purposive sampling technique i.e. by considering their pretest scores. In this case, the use of pretest score was as a guide to find which student who had highest, middle, and lowest pretest scores and to analyze whether there was significant increasing mean score from their initial scores to final scores. From each pretest score level, only four students were taken as interviewees. The interviewees were then showed their pretest and posttest scores and then asked the following questions: Figure 3.2 Interview Questions Questions for the interviewees who get high gained score: Questions for the interviewees who get low gained score: ―Look Your past tense score increases so high. So, do you feel motivated to learn past tense using CALL? Why? And, do you feel easy to understand past tense using CALL? Why? ―Look Your past tense score increases just a little. So, don‘t you feel motivated to learn past tense using CALL? Why? And, don‘t you feel easy to understand past tense using CALL? Why? The answers for such questions were useful to make a conclusion and suggestions for this study.

1. The Validity and Reliability of the Test Item

A good instrument was an instrument that could fulfill criteria of test validity and reliability. In other word, the instrument had to be valid or really measure what the test maker wanted to measure and could produce consistent result when it was administered again. To check whether the instrument that was used had fulfilled the two criteria, the following statistical calculations were employed: a. Testing Item validity To examine a validity of test items, bi-serial point correlation formula was used as follow 3 : = √ Note: = coefficient of bi-serial point correlation = average score of students who answer correctly for certain item which is being examined its validity = average total score = standard deviation of total score p = proportion of students who answer correctly q = proportion of students who answer wrongly The result of the above calculation would show the value of ‗ ‘ product moment of each test item. Such value was then compared to the value of ‗r‘ product moment table with degree of freedom N-nr and significance 5. If the comparison result showed that the value of ‗ ‘ was higher than the value of ‗ ‘, the test item was considered as a valid test item. Conversely, if the value of 3 Anas Sudijono, Pengantar Evaluasi Pendidikan, Jakarta: Raja Grafindo Persada, 1996, p. 185-190