PRETEND INTELLIGENCE 81
you tell me, who was Genghis Khan?” “What is the boiling point of water?”
and so on). But others include memory span for spoken digits, vocabulary,
word defi nition, general knowledge, comprehension, and the like.
Other tests eventually followed and are still being devised. However,
although procedures of test construction have been refi ned, the funda-
mentals have remained the same. First, large numbers of candidate items
are devised by test constructors. Th ese are tried out on samples of people
of appropriate ages. Th e results then dictate which of the items should be
selected or discarded to produce the desired patterns of scores.
For example, it was assumed (and still is) that population scores should
conform to a normal distribution, as described in chapter 2. It is mim-
icked in the IQ test by including relatively more items on which an aver-
age number of the trial group passed and relatively fewer on which either
a substantial majority or minority of them passed. Th e result gives the test
a quasi- biological authenticity.
As also mentioned in chapter 2, few natu ral (biological) functions con-
form to such a simple distribution. Yet the possibility is virtually com-
pletely ignored in the IQ lit er a ture. So widespread is this view, in fact, that
nearly all the statistical analyses surrounding IQ testing (including the
so- called ge ne tic analyses) have been designed to depend upon it. Th e
falsity of the assumption must therefore raise serious questions about
those analyses.
Another assumption adopted in the construction of IQ tests is that,
as a supposed biological mea sure like physical strength, it will steadily
increase with age, leveling off aft er puberty. Th is property has been duly
built into the tests by selecting items on which an increasing proportion
of subjects in each age group passes.
Of course, there are many reasons real intelligence— however we de-
fi ne it— may not develop like that. In the case of the IQ test, however, the
assumption has produced the undesired, and unrealistic, eff ect in which
scores improve steadily up to the age of around eigh teen years and then
start to decline.
Again, this is all a matter of prior item se lection. Th e eff ect is easily
reversed by adding items on which older people perform better, and reduc-
ing those on which younger people perform better. But large- scale ge ne-
tic studies on IQ and ageing are conducted on the assumption that the
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