Intelligence
Intelligence is the intellectual capability which is marked by complex cognitive feats and high levels of motivation and self-awareness. Using intelligence, we are able to learn, form concepts, understand, apply logic and reason, recognize patterns, plan, innovate, solve problems, make decisions, retain information, and use language to communicate. It is impossible to find a single domain of human life where intelligence wouldn't matter at all.
As a construct and as measured by intelligence tests, intelligence is one of the most useful concepts in psychology and neuroscience, reliably showing correlation with a multitude of variables.
While we do not currently know of any reliable way to significantly enhance or amplify intelligence, there are many factors that can impair our cognitive abilities both long- and short-term, ranging from bad nutrition and insufficient sleep to toxic chemicals and traumatic life events.
Intelligence quotient (IQ)
Even before IQ tests were devised, there were attempts to classify people into intelligence categories by observing their behavior in daily life, but better tools were on their way. In fact, the first-ever psychometric instruments were designed to measure intelligence, including the concept of the standard deviation and factor analysis.
In 1904, British psychologist Charles Spearman observed that children's school grades across seemingly unrelated school subjects were positively correlated, and reasoned that these correlations reflected the influence of an underlying general mental ability that entered into performance on all kinds of mental tests. He suggested that all mental performance could be conceptualized in terms of a single general ability factor and a large number of narrow, task-specific ability factors. Spearman named it g, for "general factor".
The g factor itself is a mathematical construct indicating the level of observed correlation between cognitive tasks. The measured value of this construct depends on the cognitive tasks that are used. The higher the g-load of an intelligence test, the better of an intelligence measurement instrument it is. The traditional and most common way of scoring intelligence tests is converting raw scores into IQ.
An intelligence quotient (IQ) is a total score derived from a set of standardised tests or subtests designed to assess intelligence, and it shows where you stand relative to the general population. Raw test scores are transformed to a normal distribution with a mean of 100 and a standard deviation of 15, 16 or 24. This results in approximately two-thirds of the population scoring between IQ 85 and IQ 115 (when using a standard deviation of 15, or SD15) and about 2 percent each above 130 and below 70. Only one in a thousand scores fractionally over three standard deviations above the mean (~3.09 SD), higher than 99.9% of the population, and it is this level of rarity which is the admission criterion for the Triple Nine Society.
Below is a graph (the bell curve) and the table of comparison for the three different IQ scales. While SD15 is considered default nowadays, there are still tests in use that apply SD16 or SD24 instead, and you can recognize them on our test scores page by a much higher score required for qualification. We also accept a range of academic aptitude tests which are not intelligence tests and are not scored in IQ, but the g-load of these tests is high enough to consider them a reliable proxy of general intelligence.
