The above formula measure the two means of pre-test and post-test. This formula finds the significant differences between the two means. If the difference
between the two means is more than 20, it can be concluded that the Grammar Translation Method improve the students’ achievement of causative verb.
3. 5 The Instrument
In a study, instrument as a tool for collecting data plays a very significant roles in that it greatly determines the result of the study. Thus, constructing
research instrument carefully and in an appropriate manner is greatly fundamental. With regard to the different desired data, research instrument may
differ from one study to another. Research instrument may be in the forms of test, questionnaire, observation sheet, records of interview and interview sheet, etc.
According to Arikunto 2006: 166, conducting the instrument of the test is very important because the researcher could make the test valid and reliable.
Here are the procedures in conducting the instrument: 1 Planning include the goal formulation; decide the variable, variable categorization. For the test include
goal formulation and specification table making. 2 Items writing, or questioner, scale arranging, interview’s guidance arranging. 3 Editing, that is complete the
instrument with the doing guidance, covering letter, keys, etc. 4 Try out, whether in the small scale or in the big scale. The other is answers’ design,
suggestions, etc. 5 Result analysis, and items analysis; look for the observation answers’ design, suggestions, etc. 6 Conduct some revision toward the poor
items, and continue the research based on the gathered data in the try-out.
3.6.1 Try-Out
The quality of the data, whether it is good or bad, is based on the instrument used. A good instrument fulfills two important qualifications i.e.
reliability and validity. So, before the test was used as the instrument, it had been tried out first to the students in another class. The purpose of it was to collect the
data. After the result of the try-out is gained, the analysis was made to find out the validity and reliability of the items of the test. Some items remained to be used
because they were valid while some others were left out because they were invalid. The try-out of this study was conducted on Monday, February 14, 2011 to
the eleventh grade students of SMA N 1 Tunjungan.
3.6.2 Validity of the Test
Best 1995: 208 writes “validity is that guilty of a data-gathering instrument or procedure that enables it to measure what it is supposed to
measure”. Inyang 2010: 20 also defines “Validity as the ability of a research
instrument to measure what it was designed to measure. This has to do with whether, for instance, the questions formulated in a questionnaire or interview
schedule are linked to the objectives of your study”. To conduct the test validity, the writer used the formula that called Product moment.
r
xy
=
2 2
2 2
Y Y
N X
X N
Y X
XY N
In which:
r
xy
: the correlation of the score of each item
N : the number of the subjects
∑x
: the sum of the total score in each item
∑x
2
: the sum of the square of the total score in each item
∑y
: The sum of total score from each student
∑y
2
: the sum of the square of the total score from each subject
∑xy :
the sum of the multiple of the score from each subject with the total score
Arikutno, 2002: 146 After the writer obtained the reliability score, the following step was to
insult to the score with the r Product Moment table.
3.6.3 Reliability of the Test
Best 1995: 208 says that “reliability is the degree that the instrument procedure demonstrates: whatever it is measuring, it does so consistently”. It is
not too different with the Inyang’s explanation 2010: 19 Reliability as the ability
of an instrument to produce the same or similar results each time it is used to take measurements under the same or similar conditions. Research instrument that has
a high reliability is called the reliable measurement. To conduct the test validity, the writer used the formula that called KR – 20 formulas.
r
ii
=
1 k
k
t t
V pq
V
In which,
r
ii
= coefficient of each item
k = the total number of the test
V
t
= the total number of variance
P = subject proportion which answers the items accurately
Q
= subject proportion which answers the items wrongly Arikunto, 2006: 189
After the writer obtained the reliability score, the following step was to insult to the score with the r Product Moment table.
3.6.4 Difficulty Level
After the try out conducted, each of the items were classified into difficulty level by using this formula:
P = JS
B
In which:
P = item difficulty
B = number of students who answer the item correctly
JS = number of students
Arikunto:, 1995: 212 The level of difficulty of each was be determined by using these following
categorizations: P
≤ 0, 3 is difficult
0, 3 P ≤ 0, 70
is medium 0, 7 P
≤ 1 is easy
Arikunto, 1995: 214
3.6.5 Discriminating Power
The discriminating power measures how well the test items arranged to identify the differences in the students’ competence. This formula is given below:
D = JB
BB JA
BA
In which:
D = discriminating power
BA
= number of students in the upper group who answer the item correctly
BB = number of students in the lower group who answer the item correctly
JA = number of all students in the upper group
JB = number of all students in the lower group
Arikunto, 1995: 218 The criteria of the discrimination index are as follows:
D = negative is very poor
0, 00 D ≤ 0, 20 is poor
0, 20 D ≤ 0, 40 is satisfactory
0, 40 D ≤ 0, 70 is good
0, 70 D ≤ 1
is excellent Arikunto, 1995; 225
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CHAPTER IV RESEARCH FINDING AND DISCUSSION
