21 T-014
1 42
T-042 19
10
B = 19+10 = 29 Js = 42
According to the criteria, the item number 1 was medium. For the other items, I used the same formula. It could be seen on the appendix 5
4.1.1.4 Discriminating Power
I used this following formula to find the discriminating power in the transformation of the try out test.
JB BB
JA BA
D
Where: D
: the discriminating 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 all students in the upper group JB
: the number of all students in the lower group 69
. 42
29
P
47
Table 4.3 The Criteria of Discriminating Power
Interval Criteria
20 ,
,
D 40
, 20
,
D 70
, 40
,
D 00
, 1
70 ,
D
Poor Satisfactory
Good Excellent
The following is the example of computation of discriminating power. I will focus on the item number 1as the example.
Table 4.4 The Calculation of Discriminating Power
Upper Group Lower Group
No Code
Score No
Code Score
1 T-018
1 22
T-015 1
2 T-011
1 23
T-027 3
T-012 1
24 T-008
1 4
T-019 1
25 T-041
5 T-037
1 26
T-032 6
T-021 1
27 T-038
1 7
T-039 1
28 T-029
1 8
T-013 1
29 T-010
1 9
T-024 1
30 T-031
1 10
T-023 1
31 T-009
1 11
T-036 1
32 T-002
12 T-003
1 33
T-020 13
T-017 1
34 T-028
1 14
T-006 35
T-035 15
T-004 1
36 T-033
16 T-022
1 37
T-040 1
17 T-001
1 38
T-005 1
18 T-034
1 39
T-026 48
19 T-007
1 40
T-016 20
T-030 41
T-025 21
T-014 1
42 T-042
19
10 For example item number 1, there were 19 students from upper group
who answered correctly, and 10 students from lower group who answered correctly.
The computation is as follows:
428 .
21 10
21 19
D
Based on the criteria, the item number 1 was categorized as medium. The items of the pre test instruments which were used for pre test were
30 item test of 33 valid items. They were 1, 3, 4, 5, 6, 7, 8, 11, 13, 14, 15, 17, 18, 20, 22, 23, 24, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, and 39. The unused
item test were 10 numbers. They were 2, 9, 10, 12, 16, 19, 21, 25, 30, and 40. The items of the post test instruments which were used for post test were
30 items of 32 valid items. They were 3, 4, 5, 6, 7, 8, 9, 12, 13, 14, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 28, 29, 32, 34, 35, 36, 37, 38, 39, and 40. The unused item
test were 10 items. They are 1, 2, 10, 11, 15, 16, 27, 30, 31, and 33.
4.1.2 Pre Test
