Reliability And Validity
What is reliability?
Reliability refers to how consistently a method measures
something. If the same result can be consistently achieved by using the
same methods under the same circumstances, the measurement is considered
reliable.
You measure the temperature of a
liquid sample several times under identical conditions. The thermometer
displays the same temperature every time, so the results are reliable.
A doctor uses a symptom
questionnaire to diagnose a patient with a long-term medical condition. Several
different doctors use the same questionnaire with the same patient but give
different diagnoses. This indicates that the questionnaire has low reliability
as a measure of the condition.
What is validity?
Validity refers to how accurately a method measures what it is
intended to measure. If research has high validity, that means it produces
results that correspond to real properties, characteristics, and variations in
the physical or social world.
High reliability is one indicator that a measurement is valid.
If a method is not reliable, it probably isn’t valid.
If the thermometer shows different temperatures each time, even
though you have carefully controlled conditions to ensure the sample’s
temperature stays the same, the thermometer is probably malfunctioning, and
therefore its measurements are not valid.
If a symptom questionnaire
results in a reliable diagnosis when answered at different times and with
different doctors, this indicates that it has high validity as a measurement of
the medical condition.
However, reliability on its own is not enough to ensure
validity. Even if a test is reliable, it may not accurately reflect the real
situation.
The thermometer that you used to
test the sample gives reliable results. However, the thermometer has not been
calibrated properly, so the result is 2 degrees lower than the true value.
Therefore, the measurement is not valid.
A group of participants take a
test designed to measure working memory. The results are reliable, but
participants’ scores correlate strongly with their level of reading
comprehension. This indicates that the method might have low validity: the test
may be measuring participants’ reading comprehension instead of their working
memory.
Validity is harder to assess than reliability, but it is even
more important. To obtain useful results, the methods you use to collect your
data must be valid: the research must be measuring what it claims to measure.
This ensures that your discussion of the data and the conclusions you
draw are also valid.
How are
reliability and validity assessed?
Reliability can be estimated by comparing different versions of
the same measurement. Validity is harder to assess, but it can be estimated by
comparing the results to other relevant data or theory. Methods of estimating
reliability and validity are usually split up into different types.
