There are many words to keep track of when discussing logical ability and intelligence. It can be quite confusing to try to weed out the similarities and differences between tests on the market, when the vendors are using different terms to describe them. 

Let's start with the oldest and most widely used term - Intelligence. The origins of measuring intelligence with standardized tests goes back more than 100 years. Most famous is the endeavour by Alfred Binet to develop a standardized measurement for assessing students’ intellectual development, which resulted in the Stanford-Binet test (1916) which is still in use today. 

The term Intelligence Quotient (IQ), coined by William Stern, was originally intended to describe the ratio between a student’s mental and chronological age. Students who had a mental ability above their peers would get a high IQ while those who were behind got a low IQ.

Today, IQ is instead described in relation to a population. An IQ score between 85 and 115 is average, while scores below 85 or above 115 indicates intelligence below and above average respectively. The distribution of intelligence in a broad population is often assumed to be gaussian, or normal, which has a strong foundation both in empirical observations and statistical theory (i.e. the Central Limit Theorem).

It is widely accepted that Intelligence is best measured using multiple types of cognitive tasks. For example, the latest version of the Wechsler Adult Intelligence Scale (WAIS-IV), which is used by psychologists in clinical assessments, consists of 15 separate scales that together form a measurement of IQ. These scales are grouped into verbal comprehension, perceptual reasoning, working memory and processing speed. 

There are many theories of General Intelligence today, most of which stems from the work of the psychologist Charles Spearman. In his 1904 paper, he observed that performance on many cognitive tasks were correlated, and proposed that a general factor (the g factor) explained his observations. Later theories include a hierarchy of specific abilities below g, and some even challenge the assumption of one overarching factor. The idea has taken hold however, making the measurement of General Intelligence the goal of most IQ tests today.

Taking all of this into account, the definition of intelligence we adopt at Alva is inspired by David Wechsler, Howard Gardner, Linda Gottfredson and Robert Sternberg to name a few:

Intelligence is the global ability to process information, think rationally, solve problems, deal with complexity and learn efficiently from experience.

References
​Spearman, C. (1904). “General Intelligence”, Objectively Determined and Measured. The American Journal of Psychology, 15:2, 201-292.