Tuesday, October 04, 2011

Dr. Doug Detterman's bytes: Psychometric validity

I have been remiss (busy) in my posting of Dr. Doug Detterman's bytes. Here is a new one on validity

Validity is the extent to which a test measures what it is supposed to measure and predicts what it is supposed to predict. When Binet developed his intelligence test, his goal was to identify children who would not do well in school so they could be given help. To the extent that Binet's test identified such children, it was valid. In Binet's case, proving the validity of the test amounted to showing that the test predicted or correlated with school performance. (Binet was handicapped, though, since the correlation coefficient was not widely known at the time of his first test.) Note that there is no requirement to provide an explanation of why the test predicts what it was designed to predict, only that it do it. Validity provides an empirical relationship that may be absent of any theoretical meaning. Theoretical meaning is given to the relationship when people attempt to explain why the test works to produce this validity relationship.

Tests designed to predict one thing may be found to predict other things. This is
certainly the case with intelligence tests. Relationships between intelligence and many other variables have been found. Such relationships help to build a theory about how and why the test works and ultimately about the relationship of the variables studied.

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