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B. Reliability
A reliable test is consistent and dependable. If you give the same test to the same student or matched students on two different occasions, the test should yield similar result. The issue of reliability of a test may best be addressed by considering a number of factors that may contribute to the unreliability of a test. Consider the following possibilities (adapted from Mousavi, 2002, p. 804): fluctuations in the student, in scoring, in test administration, and in the test itself.
Student-Related Reliability
He most common learner-related issue in reliability is caused by temporary illness, fatigue, a “bad day,” anxiety, and other physical or psychological factors, which may make an “observed” score deviate from one’s “true” score. Also included in this category are such factors as a test-taker’s “test-wiseness” or strategies for efficient test taking (Mousavi, 2002, p. 804).
Test Reliability
Sometimes the nature of the test itself can cause measurement errors. If a test is too long, test-takers may become fatigued by the time they reach the later items and hastily respond incorrectly. Timed tests may discriminate against students who do not perform well on a test with a time limit. We all know people (and you may be include in this category1) who “know” the course material perfectly but who are adversely affected by the presence of a clock ticking away. Poorly written test items (that are ambiguous or that have more than on correct answer) may be a further source of test unreliability.
C. Validity
By far the most complex criterion of an effective test-and arguably the most important principle-is validity, “the extent to which inferences made from assessment result are appropriate, meaningful, and useful in terms of the purpose of the assessment” (Ground, 1998, p. 226). A valid test of reading ability actually measures reading ability-not 20/20 vision, nor previous knowledge in a subject, nor some other variable of questionable relevance. To measure writing ability, one might ask students to write as many words as they can in 15 minutes, then simply count the words for the final score. Such a test would be easy to administer (practical), and the scoring quite dependable (reliable). But it would not constitute a valid test of writing ability without some consideration of comprehensibility, rhetorical discourse elements, and the organization of ideas, among other factors.
Content-Relate Evidence
If a test actually samples the subject matter about which conclusion are to be drawn, and if it requires the test-takers to perform the behavior that is being measured, it can claim content-related evidence of validity, often popularly referred to as content validity (e.g., Mousavi, 2002; Hughes, 2003). You can usually identify content-related evidence observationally if you can clearly define the achievement that you are measuring.
Criterion-Related Evidence
A second of evidence of the validity of a test may be found in what is called criterion-related evidence, also referred to as criterion-related validity, or the extent to which the “criterion” of the test has actually been reached. You will recall that in Chapter I it was noted that most classroom-based assessment with teacher-designed tests fits the concept of criterion-referenced assessment. In such tests, specified classroom objectives are measured, and implied predetermined levels of performance are expected to be reached (80 percent is considered a minimal passing grade).
Construct-Related Evidence
A third kind of evidence that can support validity, but one that does not play as large a role classroom teachers, is construct-related validity, commonly referred to as construct validity. A construct is any theory, hypothesis, or model that attempts to explain observed phenomena in our universe of perceptions. Constructs may or may not be directly or empirically measured-their verification often requires inferential data.