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Think this one through. If a measure is reliable, then can
it also be valid?
Why yes, it can. But what if it is not
reliable--for example suppose that every
time you use the
measure it varies all over the place and gives different
results.
You look at a thermometer and it reads 34, then look again a
moment
later and it reads 52, and each time the reading is different.
How can such an
unreliable measure be a valid measure? How
can a measure of such variability do
a good job of measuring
what it is supposed to measure? It cannot. Thus, a
measure must
be reliable in order to be valid. However, having reliability does
not guarantee that the measure will have validity.