The next step, the writer tried to find out the difficulty level of all items in the English Summative Test for the first grade of SMPN 3 Tangerang Selatan at odd
semester academic year 20132014 by using the following formula:
40
In which: P
: The difficulty level of all items B
: The total number of difficulty level of each item ∑
: Sigma Total N
: The total number of test items
The scale of the difficulty level of all test items ranged from 0.00 to 1.00. It can be interpreted in the rank scale of difficulty level, as follow:
40
Zaenal Arifin, loc. cit., p. 272.
’
Table 2.1 The rank scale of Level of Difficulty
41
P Interpretation
0.30 Difficult
0.30
– 0.70
Moderate 0.70
Easy
From the rank scale above, it shows the easiness and the difficultness of test items. So, the teacher will know the difficulty level of each test item in the
summative test.
b. Discriminating Power
According to J. Stanley Ahmann and Marvin D. Glock, “the discriminating power of a test item is its ability to differentiate between pupils who have achieved
well the upper group and those who have achieved poorly the lower group.”
42
Normally, the upper group will be able to answer the question well rather than the low group. The index of discriminating power is recognized by proportion if the
proportion is high it means that the test item is included in good test item because it can discriminate the upper and lower group.
As stated by Kenneth D. Hopkins, items that yield a discrimination index of .30 or more are relatively good in distinguishing between knowledgeable and less
knowledgeable examinees.
43
. The maximum size of the index is + 1.00 and the minimum size is
– 1.00. Any negative value means that the test item discriminates-to some degree-in the wrong
direction. Hence, the discriminating power of the test item is unsatisfactory. Positive
41
Suharsimi Arikunto, Dasar-dasar Evaluasi Pendidikan, Jakarta: PT. Bumi Aksara, 2006, p. 208op. cit., p. 210.
42
J. Stanley Ahmann and Marvin D. Glock, op. cit., p. 187.
43
Kenneth D. Hopkins, op. cit., p. 257.
values show that the test item discriminates in the desired direction, even though it may not be completely satisfactory.
44
At one side, a good test item is it can be answered by upper group correctly and incorrectly by lower group.
To analyze the index of discriminating power of an item, Wilmar Tinambunan states the formula as follows:
45
In which: D
: The index of item discriminating power U
: The number of pupils in the upper group who answered the item correctly L
: The number of pupils in the lower group who answered the item correctly N
: Number of pupils in each of the groups
Then, to calculate the discriminating power in short-answer item, it can be used by the formula, as follows:
46
44
J. Stanley Ahmann and Marvin D. Glock, op. cit., p. 189.
45
Wilmar Tinambunan, op. cit., p. 139.
46
Zainal Arifin, op. cit., p. 278.
D =
T =
1
X
2
X √
2 1
2 2
In which:
1
X
: The mean of upper group
2
X
: The mean of lower group
2 1
: The total quadrate of individual deviation from upper group
2 2
: The total quadrate of individual deviation from lower group n
: 27 x N upper and lower group
Table 2.2 The classifications of the index of Discriminating Power D are:
