1. Why is it important
to establish the “goodness” of measures and how is this done?
Answer
The goodness of measures
indicates whether the scale we use are reliable and valid. In other words, they
indicate to what extent we are accurately and consistently measuring the
concept (reliability), and whether we are indeed measuring whatever we are
supposed to measure (validity). If we are not measuring the intended concept
accurately, then, our study will not yield the correct results.
Reliability is
established by assessing the stability of the measure through
test-retest reliability and parallel form reliability, and internal
consistency of the measure through Cronbach’s alpha.
2. “Whenever possible, it
is advisable to use instruments that have already been developed and repeatedly
used in published studies, rather than develop our own instruments for our
studies". Do you agree? Discuss the reasons for your answer.
Answer
It is always advisable to
use well-validated instruments that have been repeatedly used in published
studies, rather than going through the cumbersome process of developing one's
own instruments and laboriously establishing their validity and reliability.
However, simply because an instrument is used in some published studies does
not necessarily make it a good instrument. It is always wise to examine the
psychometric properties established for the instrument before using it. In case
this is not easily available, a pilot study can be conducted to see if the
measures have at least acceptable reliability.
3. "A valid
instrument is always reliable, but a reliable instrument may not always be
valid". Comment on this statement.
Answer
If an instrument is valid, especially in terms of
content validity, we would expect to have a reliable instrument. However, an
instrument can have both consistency and stability, but may not be measuring
what it is intended to measure -- i.e.
have low validity. However, if an instrument does measure the concept
that it is supposed to measure, it will be reliable. Thus, a valid instrument
will be reliable, but a reliable instrument need not necessarily be valid.
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