How smart are you? This question could be asked in many different situations. For example, it might be the kind of question that is important if you are applying to college or applying for a job. In the same way that your credit score is important to anyone who might be thinking of loaning you money, an intelligence score might be interesting to anyone thinking about assigning you an important task.

That's where the idea of an intelligence quotient comes in. It is an idea that was invented nearly 100 years ago, and people have been debating its value and accuracy ever since.

An intelligence quotient is designed to be a single number that indicates a person's intelligence relative to the general population. By design, a score of 100 is meant to indicate average intelligence. Scores above 130 are said to indicate notable intelligence — perhaps 2 percent of the population has an IQ at this level.

IQ scores are determined by taking a standardized test. It is in this testing that the controversy arises. Is it even possible to measure intelligence with a test? What kind of intelligence is being measured? Is it possible to measure intelligence without introducing testing bias? And perhaps most importantly, what is intelligence?

Let's start with that last question — what is intelligence? If you look the word up at a place like http://www.dictionary.com, you will find a definition like this: "capacity for learning, reasoning, understanding, and similar forms of mental activity." Now think of the most intelligent person you know. Certainly that person is able to learn, reason and understand. But usually we think of extremely intelligent people as being able to understand deeply and then create new things. Newton created a theory of gravity. Einstein created the theory of relativity. Picasso created a new way to see the world. A gifted politician creates a new vision for the future.

Unfortunately, things like the abilities to learn, understand and create can be hard to tease apart on a standardized multiple-choice test, so an IQ test aims for something different. With an IQ test, psychologists are trying to determine a general, functional intelligence. This intelligence can be found in the abilities to solve math problems, to mentally manipulate objects in 3-D, to understand words and to answer memory questions.

The idea is that these abilities make use of general brainpower and therefore offer a view into the general intellectual abilities of a person's brain. If a person is unable to handle problems dealing with memory, language, mathematics and space, it is likely that the person has low general intelligence. Conversely, any person who handles all of these areas well is generally intelligent.

The interesting thing is that all of these areas seem to be related. That is one thing that gives IQ testing credibility. They also seem to be consistent over time. In general, a person who is good at general math problems also tends to be good with memory, language and spatial reasoning. There are exceptions, and there are also people with savant syndrome (people who excel remarkably at one thing like math, but who might not be able to fix their own breakfast). As a general rule, however, ability tends to apply across the board, and over the course of a lifetime. By creating a test with a good mix of questions, the idea is that testing bias, misunderstandings and individual variations even out to create a good score of general intelligence.

There are many things an IQ test cannot measure. An IQ test is blind to things like how much you know, how well you express yourself or how creative you are. This is why some college entrance exams now include an essay portion. This is a way of delving into things like creativity and expressiveness, at least in the written realm.

Will there ever be a perfect IQ test? Probably not. But modern tests can be very good at assessing general intelligence in a finite amount of time, because psychologists have had nearly a century to test millions of people and work out many of the kinks.

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