36
880 .
106 50
50 930
22642
2
= −
= S
⎟ ⎠
⎞ ⎜
⎝ ⎛
− ⎟
⎠ ⎞
⎜ ⎝
⎛ −
= 880
. 106
710 .
4 880
. 106
1 30
30
11
r
989 .
=
From the computation above, the writer got some results. First, the writer computed
∑pq The sum of the result p x q, the result was 4.71. s Standard deviation of the test, the result was 106.880. Then the writer took it into this
formula, and the result was 0.989. In
α = 5 with n = 40, so r
table
= 0,316 because r
11
r
table
, so that instruments is reliable.
4.1.3 Index of Difficulty
The index of difficulty level is generally expressed as the percentage of the students who answered the item correctly. The writer used this formula of index
difficulty:
P=
JS B
Where: P : index of difficulty
B : number of the students who answered item correctly. JS : number of the students in a class.
37
Criteria ID interval
Criteria 0.00 ID
≤ 0.30 0.30 ID
≤ 0.70 0.70 ID 1.00
difficult medium
easy The computation item no.1
Upper group Lower group
No code score No code
score 1 UC-1 0 1 UC-21
2 UC-2 1 2 UC-22
3 UC-3 1 3 UC-23 1
4 UC-4 1 4 UC-24 1
5 UC-5 1 5 UC-25 1
6 UC-6 1 6 UC-26 1
7 UC-7 1 7 UC-27 1
8 UC-8 1 8 UC-28 1
9 UC-9 1 9 UC-29 1
10 UC-10 1 10 UC-30
1 11 UC-11
1 11 UC-31 12 UC-12
0 12 UC-32 13 UC-13
1 13 UC-33 1
14 UC-14 1 14 UC-34
1 15 UC-15
1 15 UC-35 1
16 UC-16 1 16 UC-36
1 17 UC-17
1 17 UC-37 1
18 UC-18 1 18 UC-38
1 19 UC-19
1 19 UC-39 1
20 UC-20 1 20 UC-40
total 18 total 15
825 ,
40 15
18 =
+ =
P
From the computation above, the writer divided students in two groups. They were upper group was 18 and lower group was 15. Then the writer took it
into this formula with counted up upper group and lower group and divided with number of students, the results was 0.825.
38
According the criteria above, so item no. 1 has difficulty level is easy.
4.1.4 Discriminating Power
The index of discriminating told us whether those students who performed well on the whole test tended to do well or unwell on each item in the test. Discriminating
power can be obtained by using this following formula:
Where: DP : Discriminating Power
JB
A
: number of student in upper group who answered the item correctly JB
B
: number of student in lower group who answered the item incorrectly JS
A
: number of students in upper group. Criteria
DP interval Criteria
0.00 DP ≤ 0.20
0.20 DP ≤ 0.40
0.40 DP ≤ 0.70
0.70 DP ≤ 1.00
poor satisfactory
good excellent
The computation item no.1: Upper group
Lower group No code
No code No
code 1
UC-1 0 1 UC-21 2
UC-2 1 2 UC-22 3
UC-3 1 3 UC-23 1
4 UC-4 1 4 UC-24
1 5
UC-5 1 5 UC-25 1
6 UC-6 1 6 UC-26
1
A B
A
JS JB
JB DP
− =
39
7 UC-7 1 7 UC-27
1 8
UC-8 1 8 UC-28 1
9 UC-9 1 9 UC-29
1 10 UC-10
1 10
UC-30 1
11 UC-11 1
11 UC-31
12 UC-12 12
UC-32 13 UC-13
1 13
UC-33 1
14 UC-14 1
14 UC-34
1 15 UC-15
1 15
UC-35 1
16 UC-16 1
16 UC-36
1 17 UC-17
1 17
UC-37 1
18 UC-18 1
18 UC-38
1 19 UC-19
1 19
UC-39 1
20 UC-20 1
20 UC-40
total 18 Total
15
15 ,
20 15
18 =
− =
DP
From the computation above, the writer divided students in two groups. They were upper group was 18 and lower group was 15. Then the writer took it
into this formula with subtract 15 from 18 and divided with number of students in upper group, the results was 0.825.
According the criteria above, so item no. 1 has difficulty level is poor.
4.2 The Significant Difference of Pre Test Results
