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a. Validation
To have valid and reliable instrument, it was important to test validity and reliability of the instruments. Firstly, validity was a
precise degree between data from the respondents and obtained data from the researcher Fraenkel, 2012. It involved the degree in which
the content domain associated with the construct. In this case, validity test was used to measure the instrument whether it is valid or invalid.
Secondly, reliability test was used to measure the consistency of measurement tool in a certain research.
1.
The Validity of Instrument
The appropriateness of the test could be achieved by using Pearson Product Moment formula to calculate the validity and Alpha
method in calculating its reliability. The formulation was in the following:
Table 3.5 The Formula of Product Moment
] .
][ .
[ .
2 2
2 2
i i
i i
i i
i i
i
Y Y
n X
X n
Y X
Y X
n r
Note :
i
r
= time score result X and Y for each respondent
X
= score of test instrument X
Y
= score of test instrument Y
2
X
= quadratic score instrument X
2
Y
= quadratic score instrument Y n = number of respondent
To judge the validity of each item could be seen from the coloumn corrected item-total correlation r
count
compared with r
table
. If r
count
r
table
that item wa s valid or otherwise using α=0.05. Based on
trying out instrument which was conducted to 35 respondents of with 28 statemen
ts related to students‟ reading interest, it was obtained that 23 statements were valid and 5 statements were invalid. It can be seen
on the table 3.7 as follows.
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Table 3.6 Validity Test Item
r-count r-table
Status
1
0.080 0.334
Drop
2
0.366 0.334
Valid
3
0.440 0.334
Valid
4
0.520 0.334
Valid
5
0.591 0.334
Valid
6
0.484 0.334
Valid
7
0.378 0.334
Valid
8
0.063 0.334
Drop
9
0.431 0.334
Valid
10
0.415 0.334
Valid
11
-0.220
0.334 Drop
12
0.537 0.334
Valid
13
0.507 0.334
Valid
14
0.347 0.334
Valid
15
0.364 0.334
Valid
16
0.759 0.334
Valid
17
0.731 0.334
Valid
18
0.530 0.334
Valid
19
0.654 0.334
Valid
20
0.450 0.334
Valid
21
0.428 0.334
Valid
22
0.604 0.334
Valid
23
0.538 0.334
Valid
24
0.595 0.334
Valid
25
0.490 0.334
Valid
26
0.403 0.334
Valid
27
0.083 0.334
Drop
28
-0.041 0.334
Drop
Based on the table above, it can be seen that there were 5 numbers of item which were invalid, number 1, 8, 11, 27, and 28 see appendix
1.
2. The Reliability of Instrument
Reliability test conducted to determine the consistency of the interval among the variables and instruments. The point about item
tested was matter which valid. Looking for reliability interval method
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