The parting of the ways

We have outlined two approaches to measuring intelligence. The IQ route involves, essentially, computing an average test score in much the same way as we construct other indices. The other approach, using factor analysis, remains something of a mystery at this stage whose depths remain to be explored. It is now time to stand back and view the problem of measuring intelligence from first principles and then to form a judgement on the best way forward. Our conclusion will be that the emphasis on IQ in the past has been misplaced and that, in an ideal world, it would be abandoned. However, there seems little chance of that happening. So it is worth seeing whether a reasonable justification for its use can be given and whether the objections raised against it are well founded. This will also pave the way for the introduction of its main competitor, g. Our strategy in this chapter is, therefore, to expose the weaknesses of the ‘index’ approach by making the best case for it that we can!

Such an evaluation certainly cannot be made effectively from a purely historical perspective, because the concepts on which the measurement of intelligence depends have only emerged slowly over a century. Indeed, much of the current confusion arises from a lack of clarity about the conceptual framework – often because the protagonists have adopted the outlook of the pioneers and failed to take new work on board.