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3.6.3 Discriminating Power of Writing Test
Item of discriminating power shows how well an item performs in separating the better student to the poorer student. There are two main steps to calculate the
index discrimination. First, the result scores of the try-out are arranged by well organizing the student’s result from the highest to the lowest scores. Then,
categorize all students who take tests in two groups: upper and lower groups by taking 50 from the highest score as upper and 50 from the lowest score as
lower group. To find out the discrimination index of the writing test, the following is
used: Where,
t = t-test
M
H
= the mean of the upper group M
L
= the mean of lower group ΣX
1 2
= the sum of the upper group deviation ΣX
2 2
= the sum of the lower group deviation n1
= the number of subjects in upper and lower group Arikunto, 2002: 278. After getting the t-value, each number of items is then checked critical
value of t-table. Thus, if the obtained t-value is bigger than t-table, the item is said to be able to discriminate power. The completed computation of it can be seen in
appendix 4 and 7.
⎟⎟⎠ ⎞
⎜⎜⎝ ⎛
− ΣΧ
+ ΣΧ
= 1
n n
ML -
MH t
1 1
2 2
2 1
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3.6.4 Difficulty Level
The difficulty level of a test item indicates the percentages of students who get the item right. The more difficult an item, the lower of the index is achieved. In the
contrary, the easier an item, the higher index is achieved. To measure the item difficulty, the following formula is used:
P = the difficulty index of each scoring criteria of writing test B = the number of subject answer correctly
Js = total number of subject Arifin, 1991:135. Thus, the index difficulty will appear as follows:
Level Criteria 0 – 0,30
0,31 – 0,70 0,71 – 1,0
Difficult Medium
Easy Table 3.1 The criteria of difficulty level of writing test
The index of difficulty level of an item shows how easy or difficult a particular item proved on the test. The example of computation of difficulty level
can be seen in appendix 4 and 8.
3.6.5 Scoring Technique of the Writing Test