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The result of the computation showed that the estimated r-value was 0.834. Then, based on the table of critical r-value with significant level 5 for N=
30 is 0.361. Then, due to the fact that the result of the computation was higher than the critical r-value, it could be considered that the instrument was reliable.
3.6.3 Item Difficulty
The item difficulty of test shows how easy or difficult the test items proved in the test. In order to compute item difficulty, the formula used is :
ID = Gronlund, 1982:102
Where; ID : Index of difficulty of item
RU : the number of students in the upper group who answered the item correctly.
RL : the number of students in the lower group who answered the item correctly.
T : The total number of students in both the upper group and the
lower group. According to Arikunto 2008:210, the item difficulty of the test is
classified into 3 levels; difficult, medium, and easy. In which the number in the upper group who answered the item correctly,
0.0 ID ≤ 0.30 is said to be difficult
0.30 ID ≤ 0.70 is said to be moderate
0.70 ID ≤ 1.00 is said to be easy
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After computing the overall 30 items of try out test, it was found that 3items were categorized to be easy, 26 items were categorized to be moderate, and
1 item were categorized to be difficult.
3.6.4 Item Discrimination
The discriminating power will measure how well the test items arranged to identify the differences in the students’ competence. The formula used in this study is:
DP = Gronlund, 1982:103
Where: DP :
the discrimination
index. RU : the number of students in upper group who answered the item
correctly. RL
: the number of students in lower group who answered the item correctly.
2 1
T : the number of students on one group.
The criteria of the discriminating power as follow: D
≤ 0.20 is said to be poor 0.20 D
≤ 0.40 is said to be satisfactorymedium 0.40 D
≤ 0.70 is said to be good 0.70 D
≤ 1.00 is said to be excellent Gronlund
1982:103 From the computation, it was found that 18 items were said to be good, 8
items were said to be satisfactory, and 4 items were said to be excellent.
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Based on the analysis of validity, reliability, discriminating power, and difficulty level, it could be considered that 20 items were applicable for this
study. They were numbers 1,4,7,8,9,10,11,12,13,14,16,18,19,21,22,23,25,26,28, and 29.
3.7 The Execution of the Experiment
