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The Science Of IQ Testing

Can you intelligence be measured by IQ tests?

Yes. Intelligence can be measured, and a scientific IQ test measures it well. IQ tests are the most well-researched and validated of all psychological tests and assessments. Spearman’s discovery, in 1904, of a general intelligence factor (G) common to many different mental abilities such as reasoning, general knowledge and vocabulary, has always been replicated in data sets involving large numbers of people taking a variety of mental tests.

G can be factored into fluid intelligence (Gf) – which is your  ‘on the spot’ reasoning and problem solving ability that does not depend on background knowledge or expertise – and crystallized intelligence (Gc) – which is your ability to apply learned skills, knowledge & expertise. IQ tests can accurately measure both. In fact, in general both Gf and Gc are highly correlated. If you know someone’s fluid IQ level, you can accurately predict their general IQ level (G).

 

Types of IQ test

There are a number of different  intelligence tests and subtests used in IQ testing. Crystallized intelligence (Gc) subtests  require specific cultural knowledge (e.g. vocabulary, mathematical, or factual knowledge). Fluid intelligence (Gf) subtests, that do not depend on acquired knowledge, may require seeing abstract relationships in series of shapes, or doing logical reasoning.

Our recommended free online IQ tests [link] for measuring your IQ before and after training with HighIQPro  are fluid intelligence tests. It is fluid intelligence that our IQ software targets.

 

The IQ bell curve and standardized tests

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 of scores in the general population follows a bell curve. Most people cluster around the average – between 85 and 115 IQ points. This is classified as a ‘normal’ IQ. A few individuals 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’.

 

 

 

What is an IQ standard deviation?

In basic terms, the standard deviation is a measure of the spread of the IQ bell curve distribution. In most IQ tests 1 standard deviation is 15 IQ points on a standardized IQ test. Some IQ tests (e.g. the Stanford-Binet Intelligence scales) have a standard deviation of 16. Because of this, you need slightly higher scores to match the same percentiles as tests with sds of 15.

As a rule of thumb about 2/3 of the population scores 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. In theory only 1 in 3.33 million have an IQ this high!

 

3 scientific criteria for all good IQ and psychometric tests

The online IQ tests we recommend for assessing your pre- and post-HighIQPro training have three properties that are important for all IQ and psychometric tests: they are standardized, reliable and valid.

  • Standardization. This means that the test is distributed as a bell curve with a known average and standard deviation in the population, so that comparisons of individual scores are meaningful.
  • Reliability. A reliable test is one that is consistent – either internally (different IQ questions or sub-tests should all measure the same thing), or over time – so that if you re-test someone using the same test, it should give you the same measure. If you score 120 on one day and 140 on the next, this is not a reliable test.
  • Validity. If a test is valid it measures what it is supposed to – our real intelligence (or general cognitive ability) and not ‘IQ test taking’ or ‘schooling’. This is partly established in terms of what intelligence-requiring outcomes in real life (e.g. educational achievement and career success) IQ tests can predict. IQ tests are very good at predicting real world outcomes. For a more extensive list of what IQ scores can predict, see the bottom of this page.

 

Official IQ tests administered by certified psychologists

The tests listed below are widely used by professional psychologists and test administrators.  High IQ societies will often only accept IQ scores from professionally administered IQ tests such as these to ensure that your IQ score is the real deal!

 

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. We have selected the online tests that meet the relevant criteria to accurately measure your true IQ.

 

What IQ tests can predict statistically?

The following data is taken from Grady Tower’s article ‘Theories of Multiple Intelligence’ from the The Prometheus Society‘s Journal, Gift of Fire Issue No. 33, September 1988 [link]:

A score obtained from a conventional IQ test can be used to predict performance on many activities outside the classroom. As evidence for this, here is a list of factors that are positively or negatively linked with IQ.

 

POSITIVE CORRELATES:

  • Achievement motivation
  • Altruism
  • Artistic preferences and abilities
  • Craftwork
  • Creativity
  • Dietary preferences (low-sugar, low-fat)
  • Educational attainment
  • Eminence, genius
  • Emotional sensitivity
  • Extra-curricular attainments
  • Health, fitness, longevity
  • Humor, sense of
  • Income
  • Interests, breadth and depth
  • Involvement in school activities
  • Leadership
  • Learning ability
  • Linguistic abilities (including spelling)
  • Logical abilities
  • Marital partner, choice of
  • Media preferences (newspapers, TV channels)
  • Memory
  • Migration (voluntary)
  • Military rank
  • Moral reasoning and development
  • Motor skills
  • Musical preferences and abilities
  • Occupational status
  • Occupational success
  • Perceptual abilities (for briefly-presented material)
  • Practical knowledge
  • Reading ability
  • Social skills
  • Socio-economic status of origin (parental)
  • Socio-economic status (achieved)
  • Sports participation
  • Supermarket shopping ability
  • Values, attitudes

NEGATIVE CORRELATES:

  • Accident-proneness
  • Acquiescence/obedience
  • Alcoholism
  • Authoritarianism
  • Crime
  • Delinquency
  • Dogmatism
  • Hysteria vs other neuroses
  • Impulsivity
  • Infant mortality
  • Psychoticism
  • Racial prejudice
  • Smoking
  • Truancy
  • Weight height ratio, obesity

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