In which:
r
K – R20
= Kuder Richardson Reliability n
= the number of items in the test p
i
and q
i
= the proportion of students responding correctly and incorrectly, respectively, to item I
s
2
= test variance Tuckman, 1978:163
In addition, in order to get the variance, the formula used is:
3.6.4 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:
Gronlund, 1982:102 Where:
ID = index of difficulty of item
RU = the number of students in the upper group who answer the item
correctly
r
K
–
R20
= -
=
-
ID
=
RL = the number of students in the lower group who answer the item
correctly T
= the total number of students in both the upper and the lower group
According to Arikunto 2008:210, the item difficulty of the test is classified into 3 levels; difficult, medium, and easy.
Table 1.1 Item Difficulty Criteria Interval ID
Criteria 0.0 P ≤ 0.30
0.30 P ≤ 0.70 0.70 P ≤ 1.00
Difficult Medium
Easy
3.6.5 Item Discrimination
The discrimination index of an item indicates the extent to which the item discriminates between testers, separating the more able testers from the less able.
The index of discrimination D tell us whether those students who performed well on the whole test tended to do well or badly on each item in the test.
The discriminating power will measure how well the test items arranged to identify the d
ifferences in the students‟ competence. The formula used in this study is:
Gronlund, 1982:103 DP
=
-
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 = the number of students on one group
The discriminating power of an item reported as decimal fraction. The maximum positive discriminating power is indicate by an index of 1.00. This is
obtained only when all students in the upper group answered correctly and no one the lower group did. Zero discriminating power 0.00 is obtained when equal
number of the students in each group answered the item correctly. Negative discriminating power is obtained when more students in the lower group than in
the upper group answered correctly. Both type of item should be removed and then discarded.
Table 1.2 Item Discrimination Criteria Interval D
Criteria 0.0 D ≤ 0.20
0.20 D ≤ 0.40 0.40 D ≤ 0.70
0.70 D ≤ 1.00 Poor
Satisfactory Good
Excellent
3.6.6 t-test
