The datasets for the present survey were selected with an eye to their relevance for the study of basic cognitive abilities and aptitudes. There was less interest in recovering information about tests of special achievements, such as achievements in various subjects studied in school. Indeed, in many instances variables that obviously measured such achievements were dropped from the correlation matrices before factor analysis, in order to focus attention on data for cognitive ability tests. But this was not done in all cases, and consequently some of the factors identified in my analyses can be interpreted as measures of general or special achievements. Partly as a matter of record and for reference purposes, but also for their intrinsic interest, they are considered in the present chapter.

It is hard to draw the line between factors of cognitive abilities and factors of cognitive achievements. Some will argue that all cognitive abilities are in reality learned achievements of one kind or another. Such an argument is difficult to counter, because it is obvious that the performances required on even the most general tests of intelligence depend on at least some learnings – learnings of language and its uses, of commonly used symbols such as numbers and digits, or of procedures for solving various kinds of problems.