P = 24.5 + 19.5
72 = 0.61
So, the item number 1 is medium. From the computation of all items validity, it is found that there are 3
items are easy, 5 items are medium, and 2 items are difficult.
3.5.1.1.3 Validity of the Test
Gronlund 1998:226 states that “validity is the extent to which inferences made from assessment results are appropriate, meaningful, and useful in terms of
the purpos e of the assessment.” In other words, test validity is a test that measures
what it is supposed to measure. To ensure the validity of the test, I will do two kinds of tests. The first is face validity and the second is content validity of the
test. Hughes
1989: 27 says that “a test is said to have face validity if it looks as if it measures what it is supposed to measure.” Further he states that “by
comparing the test specification with the test content, the content validity of the test can be checked. Before the test is constructed, the test specification is
made .”1989:22 This test specification provides a basis in constructing the test.
Since this is an individual judgement, strong relation between test specification
and test content determines the content validity of the test itself.
In this study, to investigate the validity of the instrument, I use Product Moment formula stated by Arikunto 2006:170. The formula is as the following:
Where: r
xy
: validity of the instrument
N : the number of the students
X : the score of each component of speaking
Y : the sum of all composition‟s score
Then the computation for item number 1 is like this below: N
: 18 ∑xy : 690.25
∑x : 44
∑y : 276
∑x
2
: 1936 ∑y
2
: 76176 So
,
r
x
y
=
r
xy
= 0.7639 r
table =
0.468 By using the Product Moment formula, I get the index validity of number
1 is 0.7639. Then I consult the table of r product moment with N= 18 and significant level 5 in which r is 0.468. Since the result of computation is higher
than r in the table, the index validity of item number 1 is considered to be valid. From the 10 items, 8 items are valid, and 2 items are invalid. The invalid items are
number 6 and 9. Those which are invalid must be rejected so those will not be used as the instrument of post test. The complete data can be seen in Appendices.
3.5.1.1.4 Reliability of the Test
