Chapter 4: Reliability and Validity
In general, a measure of behaviour is said to be reliable if its results are repeatable when
the behaviours are re-measured – reliability is essential because without it there is no way
of determining what a score on a particular measure means, for example, in reaction time
you’re trying to determine how fast someone is, but if the reaction times vary wildly,
there is no way to answer that question, it should remain consistent over time.
A behavioural measure’s reliability is a direct function of the amount of measurement
error present – if there is a great deal of error, reliability is low, and vise versa.
A behavioural measure is said to be valid if it measures what it has been designed to
measure, for example, a test of intelligence should measure intelligence and not
Content validity is concerned with whether or not the actual content of the items on a
test “makes sense” in terms of the construct being measured.
Face validity is not actually a “valid” form of validity at all – it is concerned with
whether the measure seems to be