Figure 10.5 presents a summary of scores on the five tests as a function of age.
For the moment,
note the data for early adulthood(up to age 40).
As you can see, there are modest gains on most of the tests during the participants’ 20s and 30s. Whether we measure this in terms of performance on the qualitative reasoning tasks favoured by investigators in the postformal thought school,
or in terms of more traditional psychometric techniques,
it appears that intelligence is still increasing well into adulthood.