Where all correlations between a large battery of tests are positive, as they are in the case of IQ, factor analysis will necessarily yield a general factor that accounts for this so-called positive manifold.
All test in the battery will ‘load onto’ this general factor.
Spearman: “this general factor (g) provides a complete and sufficient explanation of the correlation between tests.”
Stability and Decline of IQ
By the age of 8 childhood IQ predicts adult IQ well – your IQ score remains reasonably stable throughout life.
IQ is simply a measure of relative standing among people of your own age; so a high correlation between IQ and age 10 and age 70 does not imply that your absolute level of performance remains the same.
