c. reliability is a necessary sufficient condition for validity
Reliability and validity are two important concepts in research. Reliability refers to the consistency and stability of a measure or procedure. If a measure is reliable, it will produce consistent results each time it is used. Validity, on the other hand, refers to whether a measure or procedure actually measures what it is supposed to measure.
It is important to note that reliability is a necessary but not sufficient condition for validity. This means that a procedure or measurement cannot be valid unless it is also reliable. However, a measurement can be reliable without being valid. For example, if we decide to use height as a measure of intelligence, we may get the same height each time we carry out the measurement, which would be described as reliable. However, since height is not an indicator of intelligence, the experiment will not be valid.
In other words, a reliable measurement or procedure may produce consistent results, but if it is not measuring what it is supposed to measure, it is not a valid measurement or procedure. To ensure that a measure or procedure is valid, researchers must carefully design their studies and select measures that are appropriate for the research question they are trying to answer. They must also ensure that their measures are reliable, so that they can be confident that any differences they observe between groups are due to the variables they are measuring, and not due to measurement error or inconsistency.