Validity of the Instrument
measure the consistency among indicators in the questionnaire which is counted based on the correlation between each items. The Alpha ranges from 0 to 1. The
higher alpha means the more reliable the items of the questionnaire Setiyadi, 2006.
In line with the explaination above, George and Mallery 2009 in ‘SPSS for Windows Step by Step: A Simple Study Guide and Reference, 17.0
’ have a suggestion in evaluating the Alpha Cronbach coefficient:
0.9 = very high reliability 0.8 = high reliability
0.7 = medium reliability 0.6 = low reliability
0.5 = very low reliability Moreover, the reliability of the reading comprehension test is measured based on
Pearson Product Moment which examines the correlation coefficient of reliability between odd and even number reliability of the half test. The formula can be seen as
follows:
Explanation: r
xy
= coefficient reliability between odd and even number x
= odd number y
= even number ∑x
2
= total score of odd number
r
xy =
∑xy
√
∑ x
2
∑ y
2
∑
2
∑y
2
= total score of even number ∑xy
= total score of odd and even number
After the reliability of the half test is calculated, Spearman Brown’s Prophecy formula is used to measure the reliability of the test as a whole as follows:
Explanation: r
k
= the reliability of the whole test r
xy
=
the reliability of half test Hatch and Farhady, 1982: 247
The criteria of the reliability are: 0.90 – 1.00
= high 0.50 – 0.89
= moderate 0.00 – 0.49
= low Arikunto’s formula in scoring the students’ result of the test is used for scoring
system. The higher score would be 100
S = x 100
Explanation: S: Score of the test
R: Right answer N: Total of the items
r
k
=
2
r
xy
1
+ r
xy