The Role of Media Selecting Tex for Materials

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3.4.2 Validity of the Test

Validity is a standard or criterion that shows whether the instrument is valid or not. In this research, the validity of each item was calculated by using the product moment formula: In which, r xy : coefficient of correlation between x and y variable or validity of each item N : the number of students participating in the test Σx : the sum of score in each item Σx 2 : the sum of the square score in each item Σy : the sum of total score from each student Σy 2 : the sum of the square score from each student Σxy : the sum of multiple of score from each student with the total score in each item

3.4.3 Reliability of the Test

Reliability shows whether an instrument is reliable and can be used as a device to collect the data. To measure the reliability of the test, the writer used used the Kuder- Richardson Formula. The formula is as follows: 26 In which, r 11 = the reliability of the test n = the number of the items p = the percentage of the students who answered the items correctly q = the percentage of the students who answered the items incorrectly S 2 = variance

3.4.4 Difficulty Level

After the try out was conducted and got the result, each item is classified into difficulty level by using this formula: T R ID = In which, ID = item difficulty R = the number of the students who answered the item correctly T = the total number of the students The level of difficulty of each item was determined by using these following categorizations: Interval of difficulty level Criteria 0.00 ID 0.30 Difficult 0.30 ID 0.70 Medium 0.70 ID 1.00 Easy 27

3.4.5 Discriminating Power

The discriminating power measures how well the test items arranged to identify the differences in the students’ competence. The formula is: T RL RU DP 2 1 − = In which, DP : discriminating power RU : the number of the students in the upper group who answered the item correctly RL : the number of students in the lower group who answered the item correctly T : the total number of the students The criteria of the discrimination index are: Interval DP Criteria 0.00 DP 0.20 Poor 0.20 DP 0.40 Satisfactory 0.40 DP 0.70 Good 0.70 DP 1.00 Excellent