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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Dr. Doug Detterman's bytes: Psychometric reliability

Another of Dr. Doug Detterman's intelligence bytes.

Reliability is consistency. A measure is reliable if it provides the same measurement on repeated applications. A measurement is an attempt to estimate the value of a true score or latent trait. If it were possible to measure this true score or latent trait value exactly, the measurement would provide the same value on each measurement occasion so long as the trait remains unchanged. However, measurement is never perfect. There will always be some error. To understand the accuracy of any measure requires knowing the amount of error in the measurement.

One of the reasons so many important relationships have been found with intelligence is that they are highly reliable.

All good science begins with reliable measurement. As Pavlov put it, control
your conditions, and you will see order. This is why reliability is so important and
probably deserves even more attention than it was given here.

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Dr. Detterman's intelligence bytes: The study of human intelligence as a social science success story

One of the leading scholars and role models in the field of intelligence research is Dr. Doug Detterman. Recently I was honored to review a number of chapters of a major book on intelligence he is writing. I was extremely impressed with the readability of the draft. It will serve as an excellent and comprehensive introduction to the wide-ranging field of human intelligence.

I recently asked Dr. Detterman if I could make a series of posts of select quotes from his draft manuscript. Being the obvious educator he is, he was pleased to grant such permission. Thus, starting today I plan to make regular (as regular as I can....hopefully at least once a week) posts with intriguing or informative direct (brief) quotes from the draft chapters I have in my possession. This is the first in the series.

I have no financial interest in Dr. Detterman's book, but in the spirit of any possible "conflict of interest disclosure" I must mention that I received a very small honorarium to review sections of his book. My goal is simple - to allow readers to learn little tidbits in advance of this major work. From what I have read, most novices and experts in the field of intelligence will want to own this book once it reaches publication with a yet to be named publisher. Kudos to Dr. Detterman.

Below is the first paragraph in the draft "introduction" section.

Intelligence is the best-understood and most powerful variable in the social sciences. Sophisticated psychometric methods, developed largely for intelligence tests, are used to construct and assess modern tests. A substantial commercial industry has grown up around the development and sale of tests. Intelligence can be measured with better reliability than any other social science variable. Huge amounts of data have been collected using the tests and these data span the last century providing a database unavailable in most other areas in the social sciences. Data from individuals show strong relationships to many important social outcome measures including educational achievement, occupational success, income, and death, to name a few. The data collected also provide important information about the genetic, biological, and environmental origins of intelligence. Relationships at the country level have also been investigated showing that countries with higher mean IQs show a greater gross domestic product per person, are less religious, and show higher levels of democracy. In short, by any objective standard, intelligence is the social science success story of unrivaled proportions

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Dr. Detterman's intelligence bytes: On the history of IQ tests and theories

This is the second in the Dr. Doug Detterman's intelligence bytes. Below is a direct excerpt.

The point of view is simple to state: Intelligence tests arose because they filled a social need and still do. Through history, important decisions about peoples' lives were made by the subjective decisions of others. The history of intelligence tests is one of replacing subjective decisions of biased observers where bias was often based on family position and political influence with objective measures from more objective tests. Tests became important tools for a developing meritocracy.

This brief history will also make clear that though we know a lot about intelligence, we do not yet know exactly what it is. There are good reasons we do not know as much as we would like to about intelligence. These reasons lie in the history of the development of the intelligence test and the parallel history of the theory about intelligence. An appreciation of what we do and do not know about intelligence requires an understanding of that history.

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