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What IQ Scores Mean

10 Cautions for Interpreting IQ Scores

Last updated:
02 Jul 2006

Guidelines for Interpreting IQ Scores

There are many popular misconceptions and misinterpretations of IQ scores.  Some psychologists give IQ a "holy grail" status, whilst others see it as just another personality characteristic.  In this sense, intelligence is just one of the many individual psychological differences.  Nevertheless, intelligence remains arguably the single most critical characteristic which determines general psychological functioning across a variety of situation.

IQ testing has a history of being used for classifying and selecting people.  As such IQ tables which give labels for various IQ scores are rules of thumb and controversial.  Therefore, use these general guidelines to help interpret IQ scores:

  1. IQ does not indicate the 'value' of a person

  2. An IQ score reflects someone's level of performance on a standard set of tasks.  These tasks are designed to be indicative of a general quality called 'intelligence', which is the capacity to observe, analyze, interpret and act adaptively on information.

  3. IQ scores obtained from a certain test should not be interpreted as absolute measures of intelligence, but rather as indicators of the probable range in which the 'true' IQ lies.

  4. Use such IQ classification tables to develop an intuitive sense of the level of intellectual functionality that people with different IQ scores are likely to have.  Avoid relying on any one person's suggested IQ ratings -- instead try to "read across" several different guidelines.

  5. When measuring IQ, there is a degree of error (e.g., someone who gets an IQ score of 89 may be "normal", but just had a below par day when tested).  Larger differences (e.g., greater than 10 points) are more meaningful and reliable.  Also note that the younger a child is, the less reliable his/her IQ test scores will be.

  6. Interpretation of an IQ score should occur in the context of broader assessment, e.g., a case report based on behavior observation and interview by a psychologist or team of mental and medical health professionals.

  7. Although there is clearly some level of unreliability and invalidities in psychological testing, these tests generally provide a more accurate and reliable tool than ad hoc judgments.

  8. Remember, there is huge debate as to where "IQ" exists or whether it is better understood as consisting of sub-types of intelligence, e.g., musical intelligence, spatial intelligence, etc.

  9. Be wary that some scales may refer to "ratio IQ" (original way of calculating IQ) and other scales use "deviation IQ" (more recent and now used more widely).  Ratio IQ is based on "mental age vs. chronological age".  Deviation IQ scores deflate ratio IQ scores - they give someone an IQ based on their ranking, using a perfect bell curve distribution.  Read more...

  10. IQ scores are not closely linked to other 'desirable' qualities such as career achievement and happiness.