I know the measure intelligence and cognitive abilities, but are these abilities genetic or are they just a measurement of skills like problem solving? For example, memory is considered a sign of intellect but memory is just as much a skill (there are many books on how to improve your memory) as a genetic aspect of someone’s personality. So what is it that IQ tests measure, do they measure genetic ability or do they measure problem solving ability or it is both? A better question would be is IQ due to genetics or enviroment?
According to the Flynn effect IQ has been going up the last 100 years or so at a rate of about 3 points a decade, roughly 10-15 points a generation. I have read in other books that this means that an IQ that places you in the top 90% in 1920 would put you in the bottom third by today’s standards, which would probably border on the old definition of retardation which was an IQ of 85 (its now 70). Causes are things like better nutrition, a more complex environment, more education and things like that.
The ability to take IQ tests.
There is a general correlation between one’s ability to take tests and one’s ability to be recognized as more or less intelligent by society, but beyond that there is little agreement even within the psych and education communiities (although the psych sub-segment of bio-metrics has a lot of faith in them–it keeps those folks employed).
IQ is actually an emergent statistical property of these types of tests rather than something that was simply invented.
The real answer is that they measure “G” and subsets of “G”. That may not mean that much too you but it is the essence of the way IQ are designed. “G” is commonly called the “General Factor” of intelligence and is controversial in its applications outside of IQ tests. The subcomponents are things like spatial skills and verbal ability.
Here is the reason I am explaining this way. IQ tests are designed by complex statistical analyses including correlations. What that means is that the tests are designed around analysis of individual questions. Most people assume that test designers just sit down and come up with questions that they believe makes someone “smart”. That isn’t how it works at all.
Example: Here is a math question of moderate complexity. Analysis shows that very few people that can’t answer most easy questions can get this right and almost everyone that can answer very difficult questions can gets this right most of the time. This question will be used to differentiate people falling in the middle of the math portion of the test.
Questions and subcomponents oif the test are analyzed so that they correlate with other test questions, and provide differentiation ability over other questions.
At the end, you have this test that differentiates people on subcomponents of the test as well as the test as a whole.
An IQ score and the components that make it up are a mathmatical property that emerges and provides the ability to differentiate people along a normal curve. It isn’t right or wrong, it just is. That is the controversial part. Different tests generate this same type of “G” loading and it isn’t easy to map it to what we see in the real world.
IQ test are pretty stable for an individual over time. You don’t see someone go from an IQ score of say 110 to 140 unless something really screwy happened. IQ tests correlate extremely highly with each other. Your score on one is basically you would get on any of the professionally administered ones. They also correlate very well with tests like the SAT and ACT but they are less reliable at predicting grades.
IQ are a real property that we can measure and we can measure it different ways. Unfortunatley, no one is completely sure what that means.
As for the nature nurture thing:
IQ’s correlate fairly well within immediate families. Adopted children’s IQ’s correlate better with their biological rather than adopted parents. Better yet, identical twins seperated at birth tend to have very similar IQ’s.
As you pointed out however, IQ has been incresing at a very fast rate over the last many decades. There is no reason to believe those increses aren’t real. A lot has changed since then and people are healthier and somewhat larger physically. The learning environments are very different too.
The way to reconcile these two factors is to assume that genetics sets a range of IQ’s that an indivdual could develop and the environment (both mental and physical) determines where the individual moves within that range.
The standard deviation of most IQ tests is either 15 or 16 points. That would probably be near the upper limit of how much an individual can move upwards based on environment. Unfortunately, there are negative environmental factors that allow any range of movement downward.