With regard to the Flynn effect, my understanding is that old people do
not have their IQ scores increase with time. One quote I found is:
: A widely held hypothesis is that people lose fluid intelligence as
: they age. This phenomena is caused by comparing the IQ tests of elderly
: people with today's young people. However, when compared to the IQ scores
: of youth in their own era ( a half a century before) the IQ losses with
: age are minimal (Raven, 1992, pp. G22-G26).
However if we take this literally, and we assume a Flynn increase of
10-20 points every 30 years, it would mean that the average IQ of 45
year olds is 80-90 if we standardize the IQ of 15 year olds as 100.
Most teenagers would probably agree, but I don't think this is how
it works. My understanding is that people's IQ is relatively stable
over most of their life and then declines somewhat in the later years.
However it is all intimately tied to how the tests are scored and
normalized. It could be that the "stable IQ" results are based on
using the same tests and scoring over the years, as that is arguably
the most reliable way to do a study over that long a time period.
This method would not show a putative Flynn "IQ drop" as that would
require renormalizing the tests as the years go by.
Because the Flynn effect was not widely recognized in the past, it's
possible that some of these IQ studies weren't careful about how they
did the normalization. The page above mentions some cases in which
incautious use of test norms from different years led to spurious reports
of IQ differences. This may cause some confusion about how IQ actually
changes with age.
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