RELIABILITY AND VALIDITY
RELIABILITY
Reliability is the consistency or repeatability of a measure
For example, if I use the measurement twice (e.g. take a test twice) would my scores be the same? Reliability focuses on the consistency of the measurement. If a measurement is reliable you should get the same results if you repeat it.
With any measurement the score you get is the observed score. This score is a combination of the true score and error score. Researchers would of course like to eliminate or at least minimize the error score.
Four sources of measurement error include:
(i) Subjects - variations in their mood, physical condition, mental state, motivation
(ii) Testing - poor directions, different expressions of interest or attempts to motivate
(iii) Scoring - use of inexperienced scorers, errors in recording
(iv) Instrumentation - inaccuracies, poor tests, calibration
We can establish the reliability of a measurement by various statistical techniques all of which attempt to see the extent to which similar results can be obtained twice. One obvious method is the same day test-retest in which the same subjects are tested twice on the same day and the results compared. This method works best when the quality being measured is unlikely to be influenced by exposure to the test. In other words, there is a question whether any
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Intrigued by this, the researcher attempted to observe how often, or to what degree, these two behaviors co-occurred throughout the academic year. The researcher used the results of the observations to assess the correlation between studying throughout the academic year and shopping for gifts. The researcher concluded there was poor equivalency reliability between the two actions. In other words, studying was not a reliable predictor of shopping for