Simply stated, your Intelligence Quotient (IQ) is designed to measure your ability to learn. Therefore, an IQ test is not meant to test what you know, but rather your potential for knowing. In other words, smart is not the same as knowledgeable.

Early Tests

The first attempt at the modern IQ test was the Binet test by Alfred Binet and Theodor Simon. This test was created to allow educational institutions to identify children who might need special education because of retarded mental development. It involved such things as asking a child to compare the weights of objects, or observing as they unwrapped a piece of candy. To anyone interested in research methodology, these tests are almost laughable, but these are the humble beginnings of our attempt to understand the workings of the human mind.

Age Accountability

The test slowly evolved to account for age and its relations to mental development. It followed the formula:

IQ = (Mental Age / Chronological Age) * 100)

For example, if a certain child could do basic multiplication at the age of 4 (CA) when the average child cannot grasp the concept until age 8 (MA), that child would have an IQ of 200. Obviously, this is a gross simplification of a complex system, though it explains the basic idea.

Deviation Accountability

These tests were quite useful for measuring the intelligence quotient for children, but failed when it came to measuring adults. This is because, measurable tests of ability started to plateau between the ages of 16 - 20. After this, dividing by the chronological age simply resulted in lower and lower scores for adults. Because of this, the deviation based tests were used. These tests compared the scores for groups of people in the same age group. This system assumes that IQs will follow a normal distribution (i.e., the standard bell curve), and that the mean score is 100 with the standard deviation being approximately 15.

Scores and Their Meanings

Classifications under the Stanford-Binet test

One of the original systems for classifying people by their IQ was created by Lewis M. Terman in his book The Measurement of Intelligence. In it, he defines these generalities:

Classification               IQ Score
Genius/Near Genius            140+
Very Superior                 120-140
Superior                      110-120
Normal or Average              90-100
Dullness                       80- 90
Borderline Deficiency          70- 80
Definite Feeble-Mindedness   below 70

At this time, anything below "Dullness" was further categorized. These classifications were changed because they were abused by the public (Moron! You are such an idiot!), and are now obsolete when referring to IQ.

Classification               IQ Score
Moron                          50- 69
Imbecile                       20- 49
Idiot                        below 20

Wechsler Adult Intelligence Scale (WAIS)

The more modern system is the WAIS. Partially because of the negative connotations society put on the original classifications (i.e., they became insults rather than measurements), the new system was far more general in its naming scheme. It still, however, closely resembled the original:

Classification               IQ Score
Very Superior                 130+
Superior                      120-129
High Average                  110-119
Average                        90-109
Low Average                    80- 89
Borderline                     70- 79
Extremely Low                below 70

As with the old system, the WAIS further categorizes anything below borderline. Today, all of these are grouped together and are typically referred to as mental retardation, though even that is not considered PC anymore.

Classification               IQ Score
Mild                           50- 69
Moderate                       35- 49
Severe                         20- 34
Profound                     below 20