Instruments Validity
2. Instruments Validity
Validity is the most important consideration in developing and evaluating measuring instruments. Historically, validity was defined as the extent to which an instrument measured what it claimed to measure. The focus of recent views of validity is not on the instrument itself but on the
interpretation and meaning of the scores derived from the instruments. 79 Simply, it can be said that a test will be valid, if it measures accurately
what is intended to measure. Therefore, related to the study, the test was aimed to measure the students‟ vocabulary mastery. Validity has three
77 John Read, Assessing Vocabulary, Cambridge: Cambridge University Press, 2000, p. 2. 78 Harold S. Madsen, Technique in Testing, New York: Oxford University Press, 1983,
p.16. 79 DonalAryAt All, Introduction to Research in Education, 8th Edition, Canada:
Wadsworth Cangage Learning, 2010, p. 225.
distinct aspects, all of which are important. There are: content validity, face validity, and construct validity. 80
a. Content validity
A test is said to have content validity if its content constitutes a representative sample. It refers to the extent to which the instrument represents the content of interest. In the other words, it is concerned with the question how well does the content of the instrument
represent the entire universe of content which might be measured? 81
A comparison of test specification and test content is the basis for judgment for content validity. The test was made based on the course objectives in the syllabus of seven grade of SMPS MuhammadiyahBuntok was noun. Therefore, this was valid it term of content validity.
b. Face validity
Face validity is a term sometimes used in connection with a test‟s content. Face validity refers to the extent to which examinees believe the instrument is measuring what it is supposed to measure. 82
The test was suitable to others and at the same level that was Junior High School level. The face validity of the test items as follow:
1) The test was about noun.
2) The forms of test items were Multiple Choice.
80 Arthur Hughes, Testing for Language Learners, Cambridge: Cambridge University Press, 1989, p. 22.
81 DonalAryAt All, Introduction to Research in Education, 8th Edition, Canada: Wadsworth Cangage Learning, 2010, p. 214.
82 Ibid, p. 228.
3) The Language of items using English.
4) The test items were suitable to the Junior High School.
c. Construct validity
This type of validity assumes the existence of certain learning theories or constructs underlying the acquisition of abilities and
skills. 83 It is concerned with the extent to which a test measures a specific trait or construct. Specifically, the construct validity measures
how well does the test measure vocabulary mastery? 84 It is the type of validity that is essential for tests that are used to individuals on
certain abilities. Since the type of test is vocabulary test, the form of test is multiple choices. In this case, the test was a written test in order to measure t he students‟ vocabulary mastery which consisted of 50 items based on provision of the school. To measure the validity of the instrument, this study using formulation of product moment as
r xy = numeral of index correlation „r‟ product moment N = total sample ∑XY = amount X score and Y score
83 J. B. Heaton, Language Testing, Longman, 1987, p.154. 84 DonalAryAt All, Introduction to Research in Education, 8th Edition, Canada:
Wadsworth Cangage Learning, 2010, p. 218. 85 AnasSudijono, PengantarEvaluasiPendidikan, Jakarta: PT Raja GrafindoPersada, 2007,
p. 219.
∑X = amount X score ∑Y = amount Y score
To know the validity level of the instrument, the result of the test will interprets to the criteria coefficient correlation: 86
0,00 – 0,20 = very poor validity 0,21 – 0,40 = poor validity 0,41 – 0,60 = fair validity 0,61 – 0,80 = high validity 0,81 – 1,00 = very high validity
Based on the result of the tryout test there were 50 valid items and 10 invalid items.