Type of the Study
34
2. Validity of the Instrument A test is considered valid if it measures what is intended to be measured.
According to Kurpius and Stafford 2006: 141, validity is defined as how well a test measures what it is designed to measure. It tells what can be inferred from the
test scores. The tests in this study are examined to be valid based on content and construct validity.
a. Content validity The content validity refers to the degree to which the test actually
measures, or is specifically related to the traits for which it is designed. In other words, content validity is achieved by ensuring that the content of the test fairly
samples the class or fields of situations or subject matter in question. It can be also achieved by making professional judgments about the relevance and sampling of
the content of the test to a particular domain. On this type of validity, the instrument must show that it fairly and comprehensively covers the domain or
items that it assess to cover. The simple present and simple past tenses mastery test in this research employed content validity. It means that the test is developed
in reference to the competency standard and basic competency of School Based Curriculum Year X of the 2
nd
semester of English Subject. 3. Reliability of Instrument
Reliability is the extent to which a test produces consistent results when administered under similar condition. A test is said reliable if it has a similar
result when it is carried out to a similar group of respondents on different occasions.
35
In this study, the researcher employed Inter-rater Reliability. It is established when the results of the simple present and simple past tenses mastery
test are assessed using subjective judgment. Inter-rater Reliability is applied to know whether the data of the score given by two assessors are reliable. The first
rater is the researcher and the second rater is a senior high school English teacher. The teacher has been teaching English for years at SMA 1 Wanadadi.
According to Johnson 2000, the simplest way to determine the degree of consistency between two scores in the scoring of a test or some other
performances measure is to have each scorer independently evaluate the test or performance measure and then compute a correlation coefficient between the
scores provided by the different scores. The formula that is used to measure the reliability is Person Product-
Moment Correlation Formula Tuckman, 1998: 275. It employed Bivarrate Correlation of SPSS 16.00