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Reliability
What is reliability? Reliability is how consistently a
test measures what it attempts to measure. Why is consistency
important? Because when you measure something with an instrument
two times, you want it to come out with the same answer (or close
to it) both times. (This is called test-retest reliability,
and it is an important measure of any kind of scientific testing.)
Personality is qualitative and therefore difficult to measure,
so psychological instruments cannot have the same consistency
you would expect from, say, a ruler. But there are generally accepted
standards for psychological instruments. The MBTI®
instrument meets and exceeds the standards for psychological instruments
in terms of its reliability.
Facts about the MBTI® instrument reliability:
- Reliability (when scores are treated as continuous scores,
as in most other psychological instruments) is as good as or
better than other personality instruments.
- On retest, people come out with three to four type preferences
the same 75% to 90% of the time.
- When a person changes type on retest, it is usually on one
of the dichotomous pairs (e.g., E-I or S-N), and in a dichotomy
where the preference clarity was low.
- The reliabilities are quite good across most age and ethnic
groups. (The T-F pair tends to have the lowest reliability of
the four scales.)
- For some groups reliability can be low, and caution needs
to be exercised in using the MBTI instrument with these groups,
e.g., children, underachieving students. When the MBTI instrument
is used with groups that are reported to have been demonstrably
lower, the results can be used as a jumping-off point for discussion.
Validity
Validity is the degree to which an instrument measures what it
intends to measure, and the degree to which the “thing”
that the instrument measures has meaning.
Why is this important? If personality type is real
(or rather, if it reflects the real world with accuracy), then
we should be able to use MBTI type to understand and predict people’s
behavior to some degree. Type should help us differentiate the
values, attitudes, and behaviors of different people.
Many studies over the years have proven the validity of the MBTI
instrument in three categories: (1) the validity of the four separate
preference scales; (2) the validity of the four preference pairs
as dichotomies; and (3) the validity of whole types or particular
combinations of preferences. Many of these studies are discussed
in the MBTI® Manual
(Consulting Psychologists Press, Inc., 1998).
Adapted from Building People,
Building Programs (chapter 7) by Gordon Lawrence
and Charles Martin (CAPT 2001).
For additional detailed research information for the MBTI
instrument,refer to the MBTI® Form M
Manual Supplement (.pdf), (Consulting Psychologists Press, Inc. 2009).
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