Intelligence Testing

Can your intelligence be measured?

Yes. Intelligence can be measured, and a standardized IQ test measures it well. IQ tests are regarded as the most accurate of all psychological tests and assessments. Spearman's discovery, in 1904, of a general intelligence factor ('G') common to many different mental abilities, has always been replicated in data sets involving large numbers of people taking a variety of mental tests. G can also be factored into fluid intelligence (Gf) - 'on the spot' reasoning and problem solving ability that does not depend on background knowledge or expertise - and crystallized intelligence (Gc) that is the ability to apply learned skills, knowledge & expertise.

Types of intelligence test

There are several different types of intelligence tests and subtests used in IQ testing. Crystallized intelligence (Gc) subtests assess words or numbers and require specific cultural knowledge (e.g. vocabulary, or mathematical or factual knowledge). Fluid intelligence (Gf) subtests may require seeing abstract relationships in series of shapes, or doing logical reasoning. Despite all the differences in these tests, they all measure in part the same general intelligence factor (G)- especially fluid intelligence subtests.

What is an IQ score? And what does my IQ mean?
The IQ bell curve & standardized IQ test explained

Individuals differ widely in their levels of intelligence. The IQ bell curve (also known as the "normal curve" in statistical jargon) describes the spread of people along the intelligence continuum, from low to high. Areas under this curve represent percentages in the population. A standardized IQ test is designed so that the average IQ level is 100, and the distribution is a bell curve. Most people cluster around the average - between 85 and 115 IQ points. This is a normal IQ. A few are either very smart or very dull. An IQ score of 130 is considered the criterion for 'giftedness'; an IQ score below 70 is considered the threshold for mental retardation. An IQ of 120 or higher is considered to be 'superior'. A score over 110 can be called a 'high normal IQ'. When a test is standardized like this, it is called a 'psychometric test'.

The IQ bell curve for IQ test scores

What is an IQ standard deviation?

What is an IQ standard deviation? In basic terms, the standard deviation is a measure of the spread of the IQ bell curve distribution. 1 standard deviation is usually 15 IQ points on a standardized IQ test. As a rule of thumb about 2/3 of the population within 1 standard deviation of either side of the average IQ score (=100). About 95% of the sample will be within 2 standard deviations from 100.

With the standard deviation and the average score, you can calculate percentiles. Percentiles tell you the percent of people that have a score equal to or lower than a certain score. These percentiles are used by high IQ societies such as Mensa to determine IQ levels for membership. The most demanding high IQ society - The PARS Society - require a proof of intelligence level at or above +5 standard deviations from the average - that is, an IQ of 175 or greater. Only 1 in 3.33 million have an IQ this high!

Professional standardized IQ tests

The tests below are widely used standardized and validated tests for intelligence. They are administered by qualified psychologists and clinicians. High IQ societies will often only accept IQ scores from a selection of these tests, administered by a professional, to ensure that your IQ score is authentic.

Free online IQ tests

There are many free IQ tests, intelligence quizzes & brain tests on the web. Most are not scientifically valid and do not measure your true IQ level. By clicking on the link below you can take one of our recommended free IQ tests with better scientific validity to answer the question 'what is my IQ?' The results of these tests are confidential.

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