IQ
What does it mean
Definition: IQ, or Intelligence Quotient, is a score derived from an intelligence test attempting to measure intelligence. Theoretically it would be a number between 0<IQ<210. Most common scores are in the 70-130 range while scores below 70 and above 130 are less common. Scores below 55 and above 145 are very rare. In this example a standard deviation of 15 is used.
Standard deviation (σ)
(graph: Gaussian bell curve or normal distribution)
The variance is the average of the squared differences between data points and the mean. Variance is tabulated in units squared. Standard deviation, being the square root of that quantity, therefore measures the spread of data about the mean, measured in the same units as the data.
|
IQ |
|||
|
SD |
(sd=16) |
sd=15) |
(sd=24) |
|
0σ |
100 |
100 |
100 |
|
1σ |
116 |
115 |
124 |
|
2σ |
132 |
130 |
148 |
|
3σ |
148 |
145 |
172 |
|
4σ |
164 |
160 |
196 |
|
5σ |
180 |
176 |
220 |
|
6σ |
196 |
190 |
244 |
Different scales
Referring to the normal distribution, different scales are used. A standard deviation of 16 is used on the Stanford-Binet scale, sd=15 is used on the Wechsler scale and a sd of 24 is used on the Cattell scale. So it is necessary to mention the standard deviation when referring to an IQ score. An IQ of 150 doesn't mean anything, an IQ 150 (sd=15) does.
The general intelligence factor
The general intelligence factor (abbreviated g) is a controversial theory to quantify what is common to the scores of all intelligence tests. This theory is mainly created by psychometrician Charles Spearman. Fluid and crystallized intelligence are a part of that theory.
Fluid and crystallized intelligence
One can distinguish two different 'types' of intelligence: fluid and crystallized intelligence (abbreviated gF and gC). Fluid intelligence is the ability to solve problems and to find patterns in chaos. It is the ability to understand the relationships between various concepts. Crystallized intelligence is the ability to use experience and knowledge. This form of intelligence applies to the long-term memory.
Genetics
The inheritance of intelligence is a grey area in science because of its complexity; intelligence cannot be defined into one single concept. One can of course say the odds that a child of intelligent parents is also intelligent are considerably larger than when the parents are mentally challenged. But currently there is none to very little evidence that (extremely) high IQ's, are inheritable.
Race & intelligence
Race & intelligence: still a very controversial issue. Because there is not enough reliable data available on the subject, we, in this society, believe that the differences in intelligence are probably caused by cultural differences combined with differences in standards of living. A person who grew up in a technologically orientated society with high standards of living (good health care etc.) would probably score higher on an IQ test than a person who grew up in an isolated tribe. These factors could explain the (very) low average scores of 3rd world countries and especially countries below the Sahara because of their very low living standards and different culture.