What Abilities are Tested on an IQ Test?
Different tests will emphasize different kinds of tasks but there has by now been enough research to identify distinct abilities. Most of this comes in the form of a kind of statistical research called "Factor Analysis." Psychologist look at the performance of large groups of people and see which kinds of tasks are related, that is, when people do well on one task, what else do they do well on, and when they do poorly, what else do they do poorly on? When they see which ones are closely related and what the tasks have in common, then it allows for a picture of what the distinct abilities are. Further research can show what each ability is related to in terms of academic achievement.
Primary Abilities
It is mostly my own distinction between what is a "Primary" ability as opposed to a "Secondary." I'm not aware of another person in psychology who has decided to distinguish categories this way, but I'm also not just making them up. For one thing, every ability has a certain amount of what we call "g Loading." The letter "g" in this case means "general intelligence" and different abilities appear to account for different amounts of g. The ones I consider Primary Abilities predict a lot of someone's IQ (they have high g loading). They also account for a lot of achievement. Finally, they tend to be closely related to each other. In fact a lot of cognitive psychology suggests they build on each other. The more of one you have, the more of the others you tend to develop. I'll explain a little more about that as we go.
Primary Ability 1, Fluid Reasoning: This is probably what most people mean when they say "Intelligence." This is the ability to solve puzzles, find patterns and figure out how things work and connect. Classic tests include matrix tasks where the student views a series of pictures and has to figure out the pattern or rule that determines what should happen next. Other tasks may have a student look at a set of figures and determine the relationships between them. Usually, these tests do not have explicitly verbal components.
In real life, we use fluid reasoning all the time. Any puzzle or problem that may make you say "OK, if when we do this, then this happens.. then I'll bet if I do THAT, then THAT will happen," is an example of fluid reasoning. Sometimes, this is related to critical thinking skills as well.
Primary Ability 2, Long-Term Memory: This is your ability to learn new things and remember what you've learned. This is a little harder to test since the kind of learning we do in real life is harder to simulate in a test and takes place over days and many repetitions. In testing, the student may learn a code, learn the names of people or things or else readily recall things that the test maker can be pretty sure the student knows.
Again, this is an ability that is used often. Especially in early schooling, we learn new words all the time and although a lot of them are sounded out, a lot of them are just learned by sight. "Island" and "right" are words that can't be sounded out, so they are learned and repeated in the same way as on Cognitive Tests.
Primary Ability 3, Fund of Knowledge: This is how much you already know. There is reasonable disagreement on whether this should be tested on IQ tests at all. Several psychologists have pointed out that relying too much on measuring Knowledge will result in low scores for students who have been through poor schooling or a home with few resources since these students will not have had the opportunity to build their knowledge. Considering that most people's idea of IQ is that it's fully or mostly intrinsic, this can make a student from a difficult background look like he or she is just not bright. Some major tests actually avoid this all together (like the CAS) while others have ways to factor it out if needed (like the KABC-II, or the WISC-V).
The problem with excluding knowledge from testing, is that it's really important. When you encounter a problem, you are more likely to be able to solve it if you have seen problems like it before. If you want to remember something, you can do so better if you can connect it to something you already know. Think for example how much easier it will be to learn the history of the revolutionary war if you already know what a "general" is, you already know about military strategy and you know the major events that led up to it. If you're reading a story, you'll understand it better if you know all of the vocabulary it uses and maybe something about the period when it was written (imagine reading Shakespeare without knowing why he keeps writing about kings). That's why Fund of Knowledge predicts a lot of achievement and why if a student has a weakness in it, I want to know it to plan on how to help. On the other hand, if a student shows a low fund of Knowledge, but is strong in the other primary abilities, then I tend to conclude that they have not had the opportunity to develop their Knowledge.
How do the primary abilities fit together?
The better your memory and learning, the bigger your fund of knowledge gets. The more you know, the easier it is to build on that knowledge to solve problems. If you remember what you figure out, then you it helps build your knowledge.
So far, there's nothing all that surprising here. While I'll get later on to whether you can specifically improve your IQ, I would say that if all you take away from this blog is that it's good to make sure you (or your child) learns a lot and gets lots of practice in solving problems, then that's great. The Secondary Abilities are maybe a bit more interesting, but they are generally not as important. They are less related to achievement, and less related to your overall score, so when a student is weak in one of them, it is more likely point to a learning disability, ADHD or other factor as opposed to a really weak IQ.
Secondary Abilities
Secondary Ability 1, Visual Spatial Reasoning: This refers to the ability make an accurate visual representation in your mind or to make sense of a visual field. People with good visual processing may be able to picture a map or a shape in their minds with great accuracy. It's that focus on whether your imagined picture is correct that makes this ability distinct from just imagining something. A child can have a good imagination and picture that he or she is flying in space, but to show that they have good visual processing, they need to be able to visualize a consistent space ship and plot its path through a map of stars we draw of them. On tests, Visual Spatial reasoning tasks might require you to assemble puzzles, plan a path through a maze, or accurately picture what an object looks like from a different angle.
There is some evidence that being particularly weak in this area can lead to poor math performance, but for the most part, it looks like as long you are at least average at this, it doesn't affect your achievement that much.
Secondary Ability 2, Auditory Processing: This is the ability to accurately analyze and understand auditory information (including speech). It's related to reading and sometimes listening comprehension. Those with poor Auditory Processing may have difficulty combining letter sounds to sound out words as they are read. It's tested with tasks that ask the student to listen to recordings of words that are hard to understand due to distortion or background noise. Other tests may require the student to distinguish among similar sounds.
Secondary Ability 3, Processing Speed: This is the ability to complete simple tasks quickly and accurately. In my experience, this is the Ability with the least helpful name. In popular use, "processing" has come to mean something like "thinking." Parents often say "he takes a while to process what I say," and then I have to explain that when they see a section of my report marked "Processing Speed" it has nothing to do with this. Rather, tests in this area require quick matching of symbols or numbers, or quickly solving simple puzzles. This is closely related to tasks like reading fluency or solving simple arithmetic where most adults and older children can work automatically. Performance on these tasks can also be affected by attention since if the student is at all distracted, they will solve fewer puzzles.
Secondary Ability 4, Short-Term Memory: Short-Term Memory is distinct from long term memory in that information is only in short term memory briefly. When you have to remember that you are in the store to buy bread, you're using your Short-Term Memory. When you first learned that bread is made from wheat, that went into your Long-Term Memory. Low scores can drag down other areas since most complex tasks are helped by being able to keep things in awareness. Short-Term Memory is also important in early reading and for mental math.
Short-Term Memory is another ability that can be impacted by difficulty in attention. Attention difficulties can mean that you miss some information before it enters Short-Term Memory, or you might become distracted while you have to keep it in awareness. Tests might be relatively simple such as having a student remember a string of letters or numbers. More complex tasks may start the same way, with a string of letters or numbers read to the student, but then the student will have to do something else. After answering other questions or otherwise being distracted, then the examiner will check whether the student still remembers the list.
Secondary Ability 5, Quantitative Reasoning: This refers to reasoning with numbers. Some tests consider this a sub ability of Fluid Reasoning, while others (such as the Stanford-Binet V) treat it as its own ability. Tests require a student to solve puzzles that require some form of counting or comparing quantities.
Quantitative Reasoning is obviously related to math ability, but becomes very hard to test in older students since it's difficult to separate from math achievement. To see whether a young child has developed the concepts of quantity, bigger or smaller, or number patterns, is easy to test with puzzles or pictures. On the other hand, if a test must challenge an older student, then the harder Quantitative Reasoning task it employs will need to be either a word problem or pictorially presented math problem. No matter how far the test moves from a straightforward math computation problem, there will be a kind of math (algebra, geometry, etc) that can be used to solve the test. This gives a very large advantage to students who have taken these classes and moves it farther away from an IQ test and into being an achievement test.