Validity Discriminating Power Try Out Analysis

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CHAPTER IV FINDINGS AND INTERPRETATION

In this chapter, the writer would like to present each of the data found in the activities. The analysis of each activity was started from the try out analysis and the tests analysis. The writer decides to give the detail explanation of each analysis to make it clear as follows:

4.1 Try Out Analysis

Try out analysis has to be done because the result of the analysis will decide which test items used in pre-test. This analysis covered the analysis of validity, discriminating power, level of difficulty, and reliability.

4.1.1 Validity

In order to measure validity for each number, the writer used Biserial Correlation formula. The formula is stated as follows: Where, r pbis = the validity of the instrument Mp = mean of the subjects who have correct answer Mt = mean of total score St = standard of deviation p = proportion of subjects answer correctly q = 1 – p q p S M M r t t p pbis − = 37 Based on the formula, the writer takes item number 1 as the sample and for the other items will use the same formula. By using that formula the writer obtain that: St = Σ Y 2 - Σ Y 2 N N M p = Sum of the subject who have correct answers Sum of the subject who have correct answers number item 1 = 1193 33 = 36.15 M t = Total score Total subject = 1278 38 = 33.63 p = proportion of subjects answers correctly Total subject = 33 40 = 0.83 q = 1 p = 1 0.83 = 0.18 38 Where, Σ Y 2 = the sum of the squared of Y scores Σ Y = the total score of correct answer N = number of students S t = 46868 - 1278 2 = 10.11 38 38 r pbis = 36.15 - 33.63 0.83 10.11 0.18 = 0.640 On α = 5 with N= 38 it is obtained = 0,321. Because of r xy r table , so the item number 1 was valid. Based the formula, the writer got 6 items were in valid. There were number 13, 23, 28, 38, 45, and 49.

4.1.2 Discriminating Power

Discriminating Power DP analysis is needed to know the discrimination between students in the upper group and the students in the lower group. The formula that the writer used to analyze the Discriminating Power is: Where, DP = the Discriminating index. RU = the number of students in upper group who answered the item correctly. T 12 RL - RU DP = 39 RL = the number of students in lower group who answered the item. ½ T = the number of students in one group. The following is the example of the computation of the discriminating power of item number 1, and for the other items will use the same formula. Table 4.1 The Computation of the DP of Item Number 1 Upper Group Lower Group No Code Score No Code Score 1 T-21 1 1 T-28 1 2 T-10 1 2 T-34 1 3 T-24 1 3 T-30 1 4 T-12 1 4 T-31 1 5 T-08 1 5 T-06 1 6 T-26 1 6 T-07 1 7 T-36 1 7 T-17 1 8 T-19 1 8 T-27 1 9 T-05 1 9 T-14 1 10 T-01 1 10 T-38 1 11 T-18 1 11 T-37 1 12 T-22 1 12 T-23 0 13 T-04 1 13 T-32 0 14 T-13 1 14 T-20 0 15 0 19 15 0 14 16 0 0 16 0 0 17 = + 17 0 18 0 0 18 0 0 19 = 0 19 0 Sum 33 Sum 25 After finding the Discriminating Power DP, the writer matched the result to the table of Discriminating Power Criteria as stated below: DP = 33 - 25 19 = 0.42 40 Interval Criteria DP 0.00 Very Poor 0.00 DP 0.20 Poor 0.20 DP 0.40 Satisfactory 0.40 DP 0.70 Good 0.70 DP 1.00 Excellent According to the criterions, the item number 1 was good because DP = 0.42. In this analysis six items were categorized very poor, there were 13, 23, 30, 38, 45, and 48. Two items were categorized poor, there were 28 and 52. Nine items were categorized good, there were 9, 17, 18, 20, 26, 33, 34, 35, and 37. Thirty nine items were categorized satisfactory, there were 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 14, 15, 16, 19, 21, 22, 24, 25, 27, 29, 31, 32, 36, 39, 40, 41, 42, 43, 44, 46, 47, 49, 50, 51, 53, 54, 55, 56. 4.1.3 Level of Difficulty In analyzing the Level of Difficulty, the writer used formula which is stated as follows: Where, ID = index of difficulty of item. RU = the number of students in upper group who answered the item correctly. RL = the number of students in lower group who answered the item correctly. T = the real number of the students. T RL RU ID + = 41 The following is the example of the computation of the level of difficulty of item number 1, and for the other items will use the same formula. Table 4.2 The Computation of the LD of Item Number 1 Upper Group Lower Group No Code Score No Code Score 1 T-25 1 1 T-16 1 2 T-21 1 2 T-28 1 3 T-10 1 3 T-34 1 4 T-24 1 4 T-30 1 5 T-12 1 5 T-31 1 6 T-08 1 6 T-06 1 7 T-26 1 7 T-07 1 8 T-36 1 8 T-17 1 9 T-19 1 9 T-27 1 10 T-05 1 10 T-14 1 11 T-01 1 11 T-38 1 12 T-18 1 12 T-37 1 13 T-22 1 13 T-23 14 T-04 1 14 T-32 15 T-03 1 15 T-02 16 T-15 1 16 T-09 1 17 T-29 1 17 T-33 1 18 T-35 1 18 T-11 19 T-13 1 19 T-20 Sum 19 Sum 14 ID = 19 + 14 38 = 0.87 After finding the Discriminating Power DP, the writer matched the result to the table of Discriminating Power Criteria as stated below: Interval ID Criteria 0.00 ID 0.30 Difficult 0.30 ID 0.70 Medium 0.70 ID 1.00 Easy 42 According to the criterions, the item number 1 was easy because ID = 0.87. In this analysis eight items were categorized difficult, there were 11, 21, 28, 35, 45, 47, 51, and 53. Twenty two items were categorized medium, there were 6, 7, 8, 9, 10, 13, 14, 15, 17, 20, 22, 25, 27, 33, 34, 37, 38, 41, 43, 46, 48, and 49. Twenty six items were categorized easy, there were 1, 2, 3, 4, 5, 12, 16, 18, 19, 23, 24, 26, 29, 30, 31, 32, 36, 39, 40, 42, 44, 50, 52, 54, 55, and 56.

4.1.4 Reliability