14, 21, 22, and 23. Then, the invalid items were not used in the pre-test See Appendix 9.
4.1.2 Reliability
To measure the reliability of the test, I applied K-R 21 by using the following formula:
;
=
the reliability of the test, = the number of items,
= the means of the scores, and = the total of variance.
The example of reliability computation could be shown as follows:
The computation of reliability obtained 0.651, for with N = 40, the r-
table = 0.312. Since r
11
was higher than r
table
0.6510.312, it was concluded that the research instrument was reliable See Appendix 10.
4.1.3 Difficulty Level
The formula used to find the difficulty level of each item was:
P=
;
in which, P
= the facility value index difficulty, B
= the number of students who answered correctly, and JS
= the total number of the students.
Table 4.1 The criteria of facility value are classified
Interval ID Criteria
0.0 ID 0.30
0.30 ID 0.70 0.70 ID 1.00
difficult medium
easy
The following was the example of the difficulty level computation of item number 4. The other items also used the same formula.
P=
P=
P= 0.65 According to the criterion, the item number 4 was medium.
From the computation of item difficulty, I found that 2 items were difficult, 15 items were medium, and 8 items were easy See Appendix 9.
4.1.4 Discriminating Power
To calculate the discriminating power of each item, I used the following formula:
D=
– ;
in which, D
= the discrimination index, BA
= the number of students in the upper group who answered the item correctly,
BB = the number of students in the lower group who answered the item
correctly, JA
= the number of students in the upper group, and JB
= the number of students in the lower group.
The following was the example of the discriminating power of item number 4. The other items also used the same formula.
D= –
D= –
D=
Table 4.2 The criteria of facility value are classified
Interval Criteria
0.0 DP 0.20
0.21 DP 0.40 0.41 DP 0.70
0.71 DP 1.00 Poor
satisfactory good
excellent
According to the criterion of discriminating power, item number 4 was satisfactory. The computation of discriminating power of the test items showed that
one item was excellent 16, 9 items were good 5, 7, 8, 9, 15, 17, 19, 24, 25, 5 items were categorized satisfactory 4, 11, 13, 18, 20, and 10 items were poor 1, 2, 3, 6,
10, 12, 14, 21, 22, 23 See Appendix 9.
4.2 The Achievement of Students’ Mastery in Pre-Test
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