ahhh, reliability and validity
Reliability and validity are concepts that many students (and researchers!) have a hard time keeping straight.
Validity: the extent to which an empirical measure adequately reflects the real meaning of the concept under consideration. (how closely do you come to hitting the bull's-eye (presumably the concept you actually want to measure?)
Reliability: whether a particular technique, when applied repeatedly to the same object, will yield the same results each time.
With that in mind, some pictures:
The "hits" are far from the bull's-eye (low validity); and all over the place (low reliability). |
Hits are closer to the bull's-eye (higher validity); but the hits are also all over (low reliability). |
Finally,
Hits are clustered in the bull's-eye-- high validity and high reliability. |
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