IQ Tests –not just a measure of general intelligence

by Gemma Craig

What does an IQ score tell you?

The concept of an IQ (intelligence quotient) test is known by scientists, psychologists and laypeople alike, and I would be surprised that if, at one point in your life, you haven’t wondered what your magic number would be.  I know I have, and I have unashamedly taken the plunge.  However, it was only recently when attending a talk hosted by Glasgow Skeptics in the pub, “Ten (quite) interesting things about intelligence tests”, I developed a need to know more (this is undoubtedly the scientist in me!).

IQ tests (if standardised, reliable and valid) capture differences between individuals’ specific cognitive abilities, such as spatial awareness or vocabulary.  Although seemingly disparate skills, it has been shown that those who perform well in one test type, perform well in others.  The positive correlation between these mental test scores indicated the influence of a dominant factor:  the general intelligence factor, g. General intelligence has been described as the combination of pre-existing knowledge and abstract reasoning to solve a variety of problems.  This general ability factor, the one source of variance common to all tests, is at the apex of a three-level hierarchy with the four intermediate factors being verbal comprehension, perceptual organisation, working memory and processing speed.

I have learned that an IQ score results from the summation of standardised scores in several tests, combining general intelligence and specific cognitive skills.  General intelligence is an important element of an IQ score, but IQ is not just a measure of general intelligence.

Like in many aspects of life, not everyone in this field shares the same opinions on the concept of a general intelligence factor.  Psychologist Stephen Jay Gould, author of The Mismeasure of Man, argued g was a mathematical artefact and criticised: …the abstraction of intelligence as a single entity, its location within the brain, its quantification as one number for each individual, and the use of these numbers to rank people in a single series of worthiness…”

What can be predicted?

The talk, delivered by Ian Deary (Professor of Differential Psychology at the University of Edinburgh), became “quite interesting” (his words), when he discussed the positive correlations between general ability, g, and aspects of an individuals’ past, present and future.

Research has demonstrated that scores achieved by children aged 11 on Cognitive Abilities Tests (CAT) strongly correlated with GCSE results achieved at the age of 16.  A correlation, along not as strong, also exists between these CAT scores and your social status, or “class”, at mid-life (based upon your house, job and car).  From four different contributing factors: (a) your father’s class, (b) your IQ at 11, (c) your education and (d) the class of your first job, the strongest correlation with your social status mid-life is your IQ at 11! This I found quite amazing!

A significant amount of research exists looking at correlations between IQ at an early age and a vast array of life aspects: later life health and mortality differences, political views and fertility!  Is it truly all about your IQ at 11??

I imagine this only represents a tiny proportion of the research out there – why not conduct your own?  If you have a friend or relative aged 11 why not test their IQ and see how they progress through life.

XX or XY?

Let’s face it; it’s what we all want to know, which of the sexes is smarter – males (XY) or females (XX)?  As the news reports annually, girls surpass boys in school performance – does this prove them to be smarter?  In actual fact, research has attributed the enhanced intellectual performance of girls to perseverance, conscientiousness and ability to self-motivate; not that females have increased general intelligence.

I am not a psychologist, nor do I claim a vast expanse of knowledge on this subject, but I’d like to share some of the things I found intriguing.  The speaker presented the graph shown in this article, which is a reflection of the widely accepted knowledge that males and females have the same average IQ, with a higher representation of males being mentally deficient or gifted.  Many believe this is due to inherent biological differences (one versus two X chromosomes) manifesting as sex differences in general intelligence or specific cognitive abilities.  From my understanding, the X chromosome plays host to the genes carrying intelligence, and carries significantly more information (or genes) compared with its smaller Y counterpart.  As such, in males, an intelligence-enhancing or mental-retardation X gene has a greater chance of becoming predominant.  If you had the choice; an average IQ or take the risk of having an IQ score at the extremes?

I discovered that the variability between males and females is greater in quantitative and visuospatial abilities, and less so in verbal; does this explain the overrepresentation of males in high-earning mathematics, science, engineering and technology focused careers?

Why not give it a go

IQ tests widely used by professional psychologists and test administrators include: Wechsler Adult Intelligence Scales, Stanford-Binet Intelligence Scales and Kaufman Brief Intelligence Test.

Off the topic (kind of)

Hopefully this article has given you an insight into IQ tests and, depending on how you want to interpret the research I’ve presented, proof that you are in fact, the smarter sex!  I was inspired to find out more about the concept of IQ after a talk hosted by Glasgow Skeptics in the pub and I’d encourage anyone, regardless of age, sex or subject of interest, to find out about upcoming talks and go along – Facebook:  Previous talks that spring to mind are “The Science of Porn” and “Why Sexed up Medicine is Bad for You”.  Add in a pint (or soft drink) followed by a lively discussion and you have the makings of an informative, but more importantly, fun, evening.

Sources used in the collation of this article:;Intelligence 30 (2002) 449–462; The Independent – Brainy sons owe intelligence to their mothers, Friday 28 June 1996; European Journal of Personality, 22, 163-166.

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0 Responses to IQ Tests –not just a measure of general intelligence

  1. Tony says:

    I joined Mensa at 18 with an IQ (according to them) of 155.
    Since then I kind of lost interest, and assumed IQ scores were no longer credible. Do you think they are a useful benchmark?

  2. I think IQ tests are fairly useful. They tend to correlate with all manner of things in the real world. Employment, educational attainment and the like.

  3. Alex Wassall says:

    I had heard that IQ tests given at age 11 correspond well with employment status and educational attainment because this is usually the first encounter one has with such a test.

    Repeated IQ testing allows subjects to become familiar with the test structure. This leads, in cases where IQ tests are used repeatedly (i.e. job interviews), to identifying those who are good at IQ tests as apposed to those with a high IQ.

    Dose this have any basis in fact?

  4. It depends on the test and how well these tests are conducted.

    IQ tests don’t have to be exactly the same questions as they test domains of general intelligence.

  5. Adrian says:

    Your right. That „magic” number, the iq score, is a result of many specific factors or mental abilities such as working memory, perceptual organisation, and so on, measured by many iq tests. But I cannot agree with the idea that an iq test taken by children can predict success later in life, success „measured” by the type of car, job or house someone own. These are simple correlations, and a correlation does not say anything about a cause-effect relation. The intelligence has its importance for getting success in life, but its only a factor among many others (emotional intelligence for instance)…

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