Validity of the Questionnaire Reliability of the Questionnaire

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3.5.1.1 Validity of the Questionnaire

According to Eichelberger 1989:117 validity addresses the extent to which a measurement process measures what a researcher wants it to measure. This characteristic of a measurement process is not inherent in the process, as is reliability, but depends on the purpose of a researcher have for the data and the way of the data are used. This study used classical pure theory formula. The formula is as follows: 2 2 Sx St rxy = rxy = validity coefficient St = student’s score Sx = the highest score Azwar, 2006:44

3.5.1.2 Reliability of the Questionnaire

Eichelberger 1989:119 mentions some statements about reliability as follows: Researchers have learned how to develop instruments and procedures in ways that maximize reliability. When most educators think about the reliability of a measure they usually think about the stability of produced over time by that measure. When quantitative data are data produced, mathematical indexes can be used to estimate the reliability of the measurement processes. 25 Therefore, reliability is the steadiness of the test. It means that students will have the similar result in the same test. Scores of students will be relatively same although students do the same test many times. This study used variance analysis technique. The formula is as follows: 2 2 1 1 Ss Se r xx − = 1 xx r = reliability coefficient Se = error variance Ss = cross subject variance Azwar, 2006:93 To make it easy, the computation of error variance can be done using formula: 1 1 2 2 2 2 − − ∑ + ∑ − ∑ − ∑ = k n nk i n Y k X i s e i = the score of a subject on an item X = the total score a subject on all items Y = the total score all subjects on an item k = the number of item n = the total number of subject Azwar, 2006:93 26 While the computation to the cross subject variance can be done using formula: 1 2 2 2 − ∑ − ∑ = n nk i k X s s i = the score of a subject on an item X = the total score a subject on all items k = the number of item n = the total number of subject Azwar, 2006:94

3.5.2 Achievement Test