The Place and Time of the Study The Method and Design of the 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 ‗ ‘ was smaller than the value of ‗ ‘, the test item was considered as an invalid test item. , the test item is valid ≤ , the test item is not valid b. Testing Item reliability To examine a reliability of test items, single test-single trial approach was used and spilt-half method was employed. This approach gave easiness since it allowed examining a reliability of a test if the test had been tried to students once. Further, the use of split-half method was for dividing the test items into two divisions. From such divisions, the correlation score of each division which was needed to find out coefficient reliability of the test was then calculated. The following was the formula to get the value of each division correlation score : 4 = √ Note: X = total score from the first division Y = total score from the second division Then, below was the formula to find out coefficient reliability of the test 5 : = Note: = Correlation score of each division = Coefficient reliability which is already suited 4 Ibid., p. 219 5 Suharsimi Arikunto, Dasar-Dasar Evaluasi Pendidikan, Jakarta: Bumi Aksara, 2006, p.93.