Growing Up, Psychology

What does an IQ of less than 105 mean for your child

I’ve added an article a while back about IQ (Coeficientul de inteligenta – IQ (Romanian)) and another one about EQ (INTELIGENTA EMOTIONALA (Romanian)) (both in Romanian unfortunately for those of you who speak only English 🙂

IQ stands for intelligence quotient. Supposedly, it is a score that tells one how “bright” a person is compared to other people. The average IQ is by definition 100; scores above 100 indicate a higher than average IQ and scores below 100 indicate a lower that average IQ.

IQ Test 4“What do you mean my child isn’t gifted — he got 99 on those tests! That’s nearly a perfect score, isn’t it?”
“The criteria you handed out says ‘a score in the 97th percentile or above.’ Peter got an IQ score of 97! That meets the requirement, doesn’t it?”

Comments like these are not unusual and indicate a complete misunderstanding of IQ test scores.

Theoretically, scores can range any amount below or above 100, but in practice they do not meaningfully go much below 50 or above 150.

Half of the population have IQ’s of between 90 and 110, while 25% have higher IQ’s and 25% have lower IQ’s:

Descriptive Classifications of Intelligence Quotients
Description X
% of Population
130+ Very superior 2.2%
120-129 Superior 6.7%
110-119 High average 16.1%
90-109 Average 50%
80-89 Low average 16.1%
70-79 Borderline 6.7%
Below 70 Extremely low 2.2%

IQ has now been used as a measure of cognitive functioning for over a century. It has played a prominent part in developmental studies in many ways: as an index of normal development; for clinical diagnostics; as a descriptor of individual differences in cognitive ability; as explanation for differences in achievement or success in the world; as a predictor of future success as in school, training and occupational selection; and as an index for exploring causes of individual differences in cognitive ability.

“there is a large and compelling literature showing that intelligence is a good predictor of both job performance and training proficiency at work” Furnam p.204

In their book, Know Your Child’s IQ, Glen Wilson and Diana Grylls outline occupations typical of various IQ levels:

140 Top Civil Servants; Professors and Research Scientists.
 130 Physicians and Surgeons; Lawyers; Engineers (Civil and Mechanical)
 120 School Teachers; Pharmacists; Accountants; Nurses; Stenographers; Managers.
110 Foremen; Clerks; Telephone Operators; Salesmen; Policemen; Electricians.
100+ Machine Operators; Shopkeepers; Butchers; Welders; Sheet Metal Workers.
100- Warehousemen; Carpenters; Cooks and Bakers; Small Farmers; Truck and Van Drivers.
90 Laborers; Gardeners; Upholsterers; Farmhands; Miners; Factory Packers and Sorters.

IQ expressed in percentiles

IQ is often expressed in percentiles, which is not the same as percentage scores, and a common reason for the misunderstanding of IQ test scores. Percentage refers to the number of items which a child answers correctly compared to the total number of items presented. If a child answers 25 questions correctly on a 50 question test he would earn a percentage score of 50. If he answers 40 questions on the same test his percentage score would be 80. Percentile, however, refers to the number of other test takers’ scores that an individual’s score equals or exceeds. If a child answered 25 questions and did better than 50% of the children taking the test he would score at the 50th percentile. However, if he answered 40 questions on the 50 item test and everyone else answered more than he did, he would fall at a very low percentile — even though he answered 80% of the questions correctly.

On most standardized tests, an IQ of 100 is at the 50th percentile. Most of our IQ tests are standardized with a mean score of 100 and a standard deviation of 15. What that means is that the following IQ scores will be roughly equivalent to the following percentiles:

IQ Percentile
65 01
70 02
75 05
80 09
85 16
90 25
95 37
100 50
105 63
110 75
115 84
120 91
125 95
130 98
135 99

An IQ of 120 therefore implies that the testee is brighter than about 91% of the population, while 130 puts a person ahead of 98% of people. A person with an IQ of 80 is brighter than only 9% of people, and only a few score less than 60.

Be cautious!

It is necessary to be very cautious in using a descriptive classification of IQ’s. The IQ is, at best, a rough measure of academic intelligence. It certainly would be unscientific to say that an individual with an IQ of 110 is of high average intelligence, while an individual with an IQ of 109 is of only average intelligence. Such a strict classification of intellectual abilities would fail to take account of social elements such as home, school, and community. These elements are not adequately measured by present intelligence tests. Furthermore, it would not take account of the fact that an individual may vary in his test score from one test to another.

Measures of intelligence may be valuable — although the value is often overrated — but much harm can be done by persons who try to classify individuals strictly on the basis of such measures alone. No one should be either alarmed or discouraged if he finds that his IQ is not as high as he might have hoped.

Remember that many elements besides IQ contribute to success and happiness.


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