To make sure that the gerund test in which the writer used in this study has good face validity of a test, she had asked her advisors to check them up. A test is
said to have empirical validity if it can show the evidence that the test scores have a high correlation to some criterion such as the mark the students got.
To measure the validity of each test item, the writer used Pearson Product Moment formula. The formula is like this:
The detailed validity of each test item can be seen in Appendix 3.
3.7.2 Reliability of the Test
Reliability of the test shows the stability of the scores when the test is used. In other words, the test measures an examinee’s ability consistently. Harris 1994: 14
says that to have confidence in measuring instruments, the researcher needs to make sure that approximately the same result will be obtained if the test is given at different
times. Based on the above point of view, the writer carried out a try-out to 28
students of IV B Regular Literature class of the English Department of UNNES in the academic year of 20062007 to get the reliability of the test items. She did four steps
to measure the reliability of the test by following the Pearson Product Moment Lado, 1975: 336.
{ }
{ }
2 2
2 2
XY
Y Y
N X
X N
Y X
- XY
N r
∑ −
∑ ∑
− ∑
∑ ∑
∑ =
First, the writer administered the test and marked each student’s test paper. The score of the try-out test can be seen in appendix 3.
The next calculations are as follows: 1
Total variance
2 The items variance
3 Coefficient reliability
This formula is used to know the value of r
11
; when r
11
r
table
the instruments are classified reliable. The detailed reliability of each test item can be
seen in Appendix 3.
3.7.3 The Index Difficulty of the Test
The index difficulty value of an item shows how easy or difficult the item test is. To determine whether the test is easy or difficult the following formula is used:
The number of the students who got bad scores
TK = The number of the students taking the test
x 100
N N
Y Y
2 2
2
∑ −
∑ =
t
σ
N N
X X
2 2
2
∑ −
∑ =
b
σ
⎟⎟⎠ ⎞
⎜⎜⎝ ⎛ ∑
⎟ ⎠
⎞ ⎜
⎝ ⎛
− =
2 2
11
- 1
1 k
k r
t b
σ σ
In which TK = Index difficulty of the test Criterion
TK Criterion 0 TK 27
Easy 27 TK 72
Sustain 72 TK 100
Difficult
The detailed index difficulty of each test item can be seen in Appendix 3.
3.7.4 The Discriminating Power
It is also important to measure the discriminating power of a test item due to the fact that it can discriminate the more able from the less able students. Heaton
states: “the discrimination index of an item indicates the extent to which the item discriminates between the testers, separating the more from the less able” Heaton,
1975:173. To measure it, the writer used this formula:
In which:
t : t-test
M
H
: Mean for upper group M
L
: Mean for lower group ∑X
1 2
: The sum of deviation scores for upper group 1
n n
x x
M -
M t
i i
2 2
2 1
L H
− ∑
+ ∑
=
∑X
2 2
: The sum of deviation scores for lower group n
i
: The number of students for upper or lower group 27 x N N
: The number of the students taking the test Criterion:
The item has the significant discriminating power if t t
table
3.8 The Administration of Real Test
