Not as much as many people think.
During my years as a consultant with families, I administered individual IQ tests to people, mostly to children, who showed signs of being intellectually gifted. I also interpreted for parents what the results mean and what the results indicate about the learning needs of their children.
This job was, for me, difficult for a variety of reasons, the foremost reason being that IQ scores aren’t precise. And I know that. Having focused on Test & Measurement for my PhD program at the University of Minnesota (once called the empiricism dustbowl for being a leader in psychological testing and analysis*), I have a different background in testing than many who administer ability tests.
IQ tests generally indicate what a person is capable of learning, not how successful or cooperative at learning — and using what’s learned — the test-taker will be.
What? IQ tests aren’t precise? Does this mean that the IQ I have for myself or my child might be wrong?
Wrong? Well, not exactly. You see, an IQ is just one sample of the range that is your “true score.” A true score is the hypothetical average of a thousand parallel testings of someone’s intellectual abilities. You can score higher or lower on any given occasion, but if you take the tests enough, the scores will find their center, the most likely place that it’s reflecting your true score or your average ability (ability to learn new things) profile and level.
Think of this: when you stick a thermometer in your mouth to get your temperature to see if you have a fever, the results vary according to which part of your mouth you stick it in, whether you’ve just had ice water or hot tea to drink, and whether you keep trying to talk while it’s in there. Because we know there’s a healthy human temperature average, we can pretty much guess if we’re doing it wrong or if the thermometer isn’t functioning correctly. (I still use this kind of thermometer and think I should get a modern one, but you get my point here).