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IQ: can intelligence really be measured?

Jacques Grégoire
Jacques Grégoire
Professor Emeritus, Faculty of Psychology and Educational Sciences, University of Louvain
Key takeaways
  • IQ is not an objective measure of intelligence. In fact, it is a relative measurement which has its own errors, measures only certain facets of intelligence and is subject to uncertainties.
  • An IQ below 70 is not synonymous with mental disability but should always be accompanied by other tests or examinations to provide a more in-depth analysis.
  • An IQ test is a clinical tool used, for example, to assess the cerebral consequences of a cranial trauma or to detect a deterioration in cognitive faculties due to ageing.
  • The measurement of IQ cannot be separated from education, social and family background or culture of origin, because intelligence is linked to these factors.
  • The average Western IQ has risen sharply since the 1940s and stabilised since the 21st Century, perhaps approaching a form of human limit.

The pur­pose of the intel­li­gence quo­tient (IQ) is to esti­mate a per­son­’s intel­li­gence, using a tool made up of a series of ques­tions: the IQ test. Tak­en in con­junc­tion with a psy­chol­o­gist, the test pro­duces a score which can be com­pared with the aver­age for the pop­u­la­tion in ques­tion, set at 100. But to what extent can IQ tests be used to assess intel­li­gence? Jacques Gré­goire, Emer­i­tus Pro­fes­sor of Psy­chol­o­gy and Psy­cho­met­rics at the Catholic Uni­ver­si­ty of Lou­vain, looks at some of the main mis­con­cep­tions sur­round­ing IQ.

IQ is an absolute measure of intelligence – FALSE

The intel­li­gence quo­tient (IQ) is some­times con­sid­ered to be an objec­tive mea­sure of intel­li­gence, but this is not the case. Intel­li­gence is a qual­i­ty that can­not be seen, so how can it be mea­sured? From the begin­ning of the 20th Cen­tu­ry onwards, researchers refined their knowl­edge of the struc­ture of intel­li­gence. This has led to the devel­op­ment of major sets of tests to assess var­i­ous facets: ver­bal, visu­al-spa­tial, work­ing mem­o­ry, etc. Cur­rent tests esti­mate an indi­vid­u­al’s intel­lec­tu­al lev­el based on the results obtained in the var­i­ous exercises.

But it should be not­ed that this is only an esti­mate. First­ly, the score is a rel­a­tive mea­sure: it defines where the indi­vid­ual stands in rela­tion to the aver­age for the group to which they belong, which is set at 100. What’s more, any mea­sure – in psy­chol­o­gy, as in any oth­er field – is sub­ject to error. This is why IQ should always be giv­en with a con­fi­dence inter­val, for exam­ple of plus or minus five points.

What’s more, an IQ test is sub­ject to many uncer­tain­ties: the con­di­tions under which the test was con­duct­ed, the objec­tive sought, the delib­er­ate or inad­ver­tent errors made, etc. As a result, it is imper­a­tive that the result obtained be accom­pa­nied by an analy­sis by a trained prac­ti­tion­er. With­out inter­pre­ta­tion, an IQ score means nothing.

A low IQ indicates a mental handicap – INCONCLUSIVE

IQ is con­struct­ed in such a way that, with­in an inter­val of plus or minus one stan­dard devi­a­tion around the mean (from 85 to 115), we find 68% of the pop­u­la­tion. Con­se­quent­ly, hav­ing a score below 100 is cer­tain­ly not a sign of intel­lec­tu­al disability.

There is, how­ev­er, a stan­dard where­by a score of two stan­dard devi­a­tions below the mean (less than 70) is con­sid­ered to be a sign of men­tal dis­abil­i­ty. But this score alone is not enough to make a diag­no­sis. It must always be accom­pa­nied by oth­er tests or exam­i­na­tions, to pro­vide a more detailed analysis.

Espe­cial­ly as the result of an IQ test can be influ­enced by many fac­tors. For exam­ple, fatigue, drug use or a psy­chi­atric con­di­tion can affect an indi­vid­u­al’s per­for­mance. This means that IQ tests are not always reliable.

Everyone needs to know what their IQ is – FALSE

An IQ test is first and fore­most a clin­i­cal tool, used to meet a spe­cif­ic objec­tive: to diag­nose men­tal dis­abil­i­ty, to assess the cere­bral con­se­quences of a cra­nial trau­ma, to detect a dete­ri­o­ra­tion in cog­ni­tive fac­ul­ties due to age­ing, and so on. The ques­tion must there­fore be of a gen­er­al nature: what is the prob­lem to be solved? The IQ test may – or may not – help to achieve this goal, but it is not an end in itself. Some peo­ple want to con­sult a pro­fes­sion­al to find out their IQ, often in the hope of obtain­ing an excep­tion­al­ly high score. But what’s the point? Even in a pro­fes­sion­al or edu­ca­tion­al envi­ron­ment, IQ is not enough to pre­dict per­for­mance. Oth­er indi­ca­tors may be more rel­e­vant, such as results in exam­i­na­tions, com­pe­ti­tions or tech­ni­cal tests. The IQ test should not be used as an absolute ref­er­ence to clas­si­fy indi­vid­u­als; that is not its purpose.

IQ test results show differences between men and women – TRUE

Just over forty years ago, IQ tests showed gen­der dif­fer­ences: girls per­formed less well on visuo-spa­tial func­tions (abil­i­ty to visu­alise in 3D an object rep­re­sent­ed in 2D) and bet­ter on ver­bal tasks. Today, these dis­par­i­ties have com­plete­ly dis­ap­peared. This means that there is no sci­en­tif­ic data to sup­port a gen­der-spe­cif­ic ori­en­ta­tion. On the oth­er hand, there is one area in which girls gen­er­al­ly obtain bet­ter results than boys: per­cep­tive speed, which reflects the abil­i­ty to spot small dif­fer­ences. This was true over forty years ago, and it remains true today.

The French have a higher average IQ than Americans – INCONCLUSIVE

The pur­pose of an IQ test is always to com­pare an indi­vid­ual with the group to which they belong, for exam­ple their com­pa­tri­ots. On the oth­er hand, it makes no sense to com­pare two dif­fer­ent pop­u­la­tions: there is cur­rent­ly no tool that can do this. In the past, some ini­tia­tives aimed to devel­op cul­ture-inde­pen­dent tests whose results would not depend on the coun­try. But this is impos­si­ble because intel­li­gence can­not devel­op out­side of culture.

This close link is some­times con­firmed in unex­pect­ed ways. Take the fol­low­ing task: hav­ing to remem­ber a sequence of num­bers and recon­struct it in reverse order. The per­fect exam­ple of an exer­cise free from any cul­tur­al influ­ence, isn’t it? Well, a pre­vi­ous study showed that one coun­try per­formed sig­nif­i­cant­ly worse than oth­er West­ern coun­tries: Lithua­nia. And why was this? In the Lithuan­ian lan­guage, most words for num­bers have two or three syl­la­bles. And work­ing mem­o­ry stor­age depends on the length of the words to be remem­bered, which is greater here than in oth­er lan­guages. So, there are many exam­ples of ques­tions that may seem uni­ver­sal, but which in real­i­ty hide major dis­par­i­ties between coun­tries. This is why any rel­e­vant test needs to be adapt­ed to each cul­ture, which requires a sig­nif­i­cant amount of work.

IQ depends on social and family environment – TRUE

Intel­li­gence, while part­ly innate, can only devel­op in a favourable con­text. School, fam­i­ly and social envi­ron­ment all play a fun­da­men­tal role. As a result, IQ can­not be mea­sured with­out ref­er­ence to edu­ca­tion or the social and fam­i­ly con­text, because intel­li­gence is linked to these. This may seem unfair, but it is a real­i­ty that can be seen in oth­er areas: the child of two top sports­men and women will more eas­i­ly devel­op ath­let­ic skills, and the same is true of the chil­dren of pro­fes­sion­al musicians.

The average IQ in France has fallen in recent years – FALSE

Thanks to com­plex sta­tis­ti­cal mod­els, it is pos­si­ble to make com­par­isons between eras. And from the 1940s onwards, there has been a fair­ly clear increase in aver­age scores in West­ern coun­tries over the decades. This is known as the Fly­nn effect. But this trend large­ly slowed down in sev­er­al devel­oped coun­tries as the 2000s approached, to the point of stag­na­tion; not regres­sion as some stud­ies with method­olog­i­cal weak­ness­es claim.

How can this phe­nom­e­non be explained? There is no absolute cer­tain­ty, but it is rea­son­able to assume that the growth in IQ was encour­aged by the improve­ment in liv­ing con­di­tions after the Sec­ond World War: low­er mor­tal­i­ty rates and child­hood ill­ness­es, more school­ing, high­er liv­ing stan­dards, etc. And in recent years, we may be approach­ing a kind of lim­it in terms of aver­age intel­li­gence. Don’t human beings have lim­its in every field?

For exam­ple, at the 1896 Olympic Games, the win­ner of the 100 m race took 12 sec­onds. Since then, this mark has been pro­gres­sive­ly improved, drop­ping below 10 s. But will a human being ever man­age to run the 100 m in under 7 or 5 s? There’s bound to be a lim­it that can­not be exceeded.

Bastien Contreras

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