Validation of Instruments PROBLEM BASED LEARNING TO ENHANCE STUDENTS’ CRITICAL THINKING SKILLS AND CONCEPT COMPREHENSION IN POLLUTION CONCEPT.

Mitha Hardianni,2013 Problem Based Learning To Enhance Students’ Critical Thinking Skills And Concept Comprehension In Pollution Concept Universitas Pendidikan Indonesia | repository.upi.edu | perpustakaan.upi.edu 5. Teacher interview The interview carried with biology teachers who teach in class that were used as research subjects. This interview is intended to find out teachers opinions toward Problem Based learning.

F. Validation of Instruments

To validate the instrument in this research, there are some steps were done as follow: 1. Instruments judgment After made the instrument, the instruments were reviewed and judged by the experts. The experts are lecturer of biology and pedagogy who expert in assessment. Based on judgment researcher got some suggestions and revision for instrument. 2. Instruments trial Before the instruments are used for research implementation, the instruments were tested to students that already learn about pollution. In this case researcher chose grade XI as trial instruments participants. 3. Instruments Analysis The instruments that are used in this research were judge and trial to other students. The result from instrument trial analyzed to get its validity, Reliability, difficulty level and discriminating power. a. Validity Based on Scarvia B. Anderson and friends “a test is valid if it measures what it purpose to measure” in Arikunto, 2012:80. “Validity refers to the appropriateness, meaningfulness, correctness, and usefulness of the inferences a Mitha Hardianni,2013 Problem Based Learning To Enhance Students’ Critical Thinking Skills And Concept Comprehension In Pollution Concept Universitas Pendidikan Indonesia | repository.upi.edu | perpustakaan.upi.edu researcher makes ” Fraenkel et al., 2012:147. To measure the validity of instruments researcher used software. Software calculation actually uses product moment correlation formula as follow Arikunto, 2012:87: r xy : correlation coefficient between test item and total score. N : number of participant X : score of the test item Y : total score Value of r xy which was obtained can be interpreted to determine validity of test item by using criteria on table 3.2 Table 3.2 Interpretation of validity of test item Value of r xy Category 0,80-1,00 Very high 0,60-0,79 High 0,40-0,59 Sufficient 0,20-0,39 Low 0,00-0,19 Very low Arikunto, 2012 b. Reliability Reliability is the provision of a test when retested to the same subject. To know this provision essentially can be seen from alignment of the result Arikunto, 2012:104. To measure test item reliability researcher used software which based on formula above Arikunto, 2012:115: Mitha Hardianni,2013 Problem Based Learning To Enhance Students’ Critical Thinking Skills And Concept Comprehension In Pollution Concept Universitas Pendidikan Indonesia | repository.upi.edu | perpustakaan.upi.edu r xx = reliability of the whole test K = number of items on the test S x 2 = variance of scores on the total test squared standard deviation p = proportion of correct responses on a single item q = proportion of incorrect responses on the same item Table 3.3 Interpretation of reliability Value of r xy Category 0,80-1,00 Very high 0,60-0,79 High 0,40-0,59 Sufficient 0,20-0,39 Low 0,00-0,19 Very low Arikunto, 2012 c. Difficulty level Difficulty level is to measure whether the test item is difficult or not. This is important to measure the difficulty level of test item because a good test item is not too easy and not too difficult for students Arikunto, 2012:222. So according to Arikunto 2012 difficulty index scale can show difficulty level of test item. To know the difficulty level of test item can use the formula below: Mitha Hardianni,2013 Problem Based Learning To Enhance Students’ Critical Thinking Skills And Concept Comprehension In Pollution Concept Universitas Pendidikan Indonesia | repository.upi.edu | perpustakaan.upi.edu P = difficulty level B = amount of student who answer question with the right answer JS = total amount of students who undertakes the test d. Discriminating power Discriminating power is ability to distinguish between lower and higher achiever from the result of test item Arikunto, 2012:226. The formula that can be used as follows: D = discriminating power JA = amount of high achiever JB = amount of low achiever BA= amount of high achiever who answers question with the right answer BB= amount of low achiever who answers question with the right answer P A = proportion of high achiever who answers question with the right answer P B = proportion of low achiever who answers question with the right answer Table 3.4 Interpretation of discriminating power Discriminating power interval Category Negative Test item is not appropriate 0.00 x ≤ 0.20 Poor 0.21 x ≤ 0.40 Sufficient 0.41 x ≤ 0.70 Good 0.71 x ≤ 1.00 Excellent Arikunto, 2012 P = D = - = P A - P B Mitha Hardianni,2013 Problem Based Learning To Enhance Students’ Critical Thinking Skills And Concept Comprehension In Pollution Concept Universitas Pendidikan Indonesia | repository.upi.edu | perpustakaan.upi.edu

G. Collecting Data Technique