Testing Instruments

1. Testing Instruments

a. Validity of Instruments

The validity refers to extend to which the result of an evaluation procedure serves the particular uses for which they are intended. There are two processes to know the validity of the instrument, they are internal validation which refers to the both validators of evaluation. The researcher asks one of qualified lectures and two English teachers to judge the validation based on the instruction stated in validation sheet. The evaluators judge all the test items with it the valid value. The content validity of the test refres to the extent to with it of the representative of the samples to the content area of the measuring instrument. The items are comparised with the score 1 that signs ―yes‖ and the evaluation scale are filled with score ―4‖ that signs the test is valid. The external validation which refers to test scores with measures of the students ability in test. The reseacher conduct try out before giving pre-test an post-test to the students.

Cohn (2005:105) argues, ―Validity is an important key effective research. If

a piece of research is invalid then it is worth less. Validity is thus a requirement of both quantitative researchers‖. Based on it, the researcher examines the validity of the

instrument by using Product Moment Correlation. It is used based on what Arikunto (1993:36) says that to know the validity of the test, the researcher uses product moment formula, as follows:

N  XY  (  X )( Y )

r xy=

 N  X    X    N  Y    Y 

Which: r xy = the coefficient between X and Y N

= the number of sample

 x = the sum of item  y = the total of score participants test

= the total score of X after quad ratted

= the total score of Y after quad ratted

 xy

= the sum of multiplication of X and Y After r xy has been known, then consulted with the value of r table to know

whether the correlation is significant or not. The significant level is 5 % (α=0,05), if r xy >r t is significant. But if the value of r xy <r t is not significant.

b. Reliability of the Instruments

Reliability is the degree of consistency with which it measures whatever it is measuring. Brown (2004:20) states, ―A reliable test is consistent and dependable.‖ In other words, the reliability indicates the consistency in measurement. A test gives the same result every time it is taken. The test is irreliable if the test result is different when the researcher is testing it again.

To obtain the reliability of the test, Brown (200:197) defines Kuder- Richardson (K-R) 21 as follows :

Note : K-R 21 = Kuder – Richardson Formula 21 K

= the number of test item S

= standard deviation ̅

= mean of the test scores Variant was quadrate of standard deviation. It means, to avoid the negative numbers that can happen when accounting the lowest score of mean, it uses quadrate

2 of quarrel to make all the number become positive. To have the total variants (s 2 t /s ), the researcher uses the formula that is taken from Djiwandono (2008: 217):

Which: s 2 = Variants

X = The score of item Ʃ = The mean of the data N = The number of the sample

c. Item Facility Analysis

According to Brown (1996:64), item facility (IF) analysis is used to find out the difficulty and easiness of items. It is statistical index used to examine the percentage of students who correctly answer a given item. To analyze it, it is used the formula as follows:

Note : IF = item facility N correct = number of students answering correctly

N total = number of students taking the test

The result of this formula is an item facility value that can range from 0.00 to 1.00 for different items. Teachers can interpret this value as the percentage of correct answers for given item (by moving the decimal point two places to the right). If the item goes to the lower percentage, the item is categorized as a difficult item because many more students miss it than answer it correctly. On the other hand, if an item goes to highest percentage, the item is categorized as an easy item because almost everyone responds accurately. Then, in the whole of the total items, 10% is difficult items, 50% is medium items and 40% is easy items.

So, the level of the item facility can be calculated as follows:

70 – 100 : easy item

50 – 69 : medium item

0 – 49 : difficult item