I previously talked about how scores on an IQ test are developed, and what they mean mathematically. Now, I’ll look at what they can mean for individuals.

IQ scores can be seen as the mind equivalent of BMI scores. Although both numbers can provide useful information when averaged across large groups, they shouldn’t be used to directly compare individuals, or used to sum up a person in one statistic. BMI can be helpful for an average-height and middling-framed Western person, but it is near-useless for athletes, who will often score as overweight or obese due to their increased muscle mass. Similarly, IQ measurements may be an accurate representation for a neurotypical person who is familiar with Western education systems and standardized testing. But they are not an accurate summation for people with neurodevelopmental disorders, or people who aren’t used to standardised tests and solving problems in a room with a stranger.

3) IQ tests cannot always measure someone’s ability accurately. Health conditions and neurological differences result in people having uneven patterns of ability, which confuse IQ tests.

Previously I said that someone with a Verbal IQ score of 119 and a Performance IQ score of 111 would have a Full-Scale (overall) IQ score of 115. In neurotypical people – those with no neurological conditions, learning disabilities, or long-term mental health conditions – IQ subscores stay together.  A neurotypical person’s general ability level is consistent across different tasks, and different types of mental processing. Their highest- and lowest-scoring skills will typically be <10 points apart, so averaging them together into one score is simple.

People with learning disabilities or neurological conditions, on the other hand, can have vast differences between their strongest and weakest skills. This can also be true for people with long-term mental health conditions: many mental health conditions, including mood and anxiety disorders, can impair people’s memory, impulse control, and ability to pay continuous attention, which are all aspects of IQ tests.

People with dyslexia may have a significantly higher Performance IQ than Verbal, while people with dyscalculia or Non-Verbal Learning Disorder often have the reverse pattern. People with autism spectrum conditions often have a “spiky” pattern of results, where individual subtest scores range from very low to very high.

For example, imagine someone who has moderate-severe dyslexia. Their high ability in nonverbal skills is unaffected by their dyslexia, so their Performance IQ is 135. Their verbal skills are significantly affected by their dyslexia, so their Verbal IQ score is 95. If their scores were averaged, the total would be 115, the same as my previous example. However, averaging scores which are this far apart would mask both the extent of that person’s strengths and the extent of their difficulties. A difference of one standard deviation (15 points) between Verbal IQ and Performance IQ is classed as medically significant, while a difference of 1.5 standard deviations (23 points) between Verbal IQ and Performance IQ means the person cannot be given a Full Scale IQ score as a single score could not fairly represent their ability and needs. This is referred to as a “non-interpretable” Full Scale IQ.

4) Having a higher IQ is not always better, and a high IQ does not guarantee success or an easy life.

Although a high IQ is associated with success up to a point, an extremely high IQ can be linked to either great successes or great difficulties. Children with an above average IQ (from 115-130) are often successful in school and popular with their peers. Beyond this point, increases in IQ come with drawbacks as well as benefits. Children with an extremely high IQ can often feel alone as they are on such a different wavelength from others. One study from 1993 found that children with an IQ of <160 felt intensely isolated for over 80% of their time in school; many felt like they had to to consciously monitor their social interactions to be accepted by others.

Another complication is twice-exceptionality – when someone has both a high IQ and a learning disability. (“High” in this context means 2 standard deviations above average, which is 130 in most tests). Twice-exception (“2e”) children are often misunderstood, as teachers can assume that a high IQ child must be uniformly skilled and may interpret the child’s difficulties as them not caring or not trying. Special education services unfamiliar with 2e may not provide any assistance to students with an average or above average overall IQ, regardless of their difficulties.

Adults with high IQ scores retain many traits common to children with high IQ, such as emotional intensity, sensitivity, seeing many sides to problems, and questioning authority. In workplaces and in adult life, these traits can be interpreted negatively; questioning authority can be perceived as rudeness, emotional intensity as moodiness or unpredictability, and seeing multiple sides as rejecting others’ viewpoints. High IQ adults can also feel isolated and unable to connect with others, which increases their risk of mental health issues. Researchers have also suggested that some high IQ adults can be misdiagnosed with ADHD or Bipolar Disorder based on their emotional intensity and sensitivity.

Ultimately, IQ is not everything. A high IQ does not guarantee brilliance or success, and it can bring someone as many difficulties as advantages. The assumptions people make about IQ, especially within education, can even prevent people from getting support and assistance when they need it.