Postscripts on premorbid ability estimation: conceptual addenda and a few words on alternative and conditional approaches.

The estimation of premorbid ability levels has been debated for some time. Some of the difficult issues involved are reviewed here and comments provided on certain approaches, some of which tend to be popular for reasons of convenience and false beliefs of their accuracy, and some that are less well-known. Demographic estimation procedures in particular tend to fare better than believed in some research. An additional approach is recommended for further research, one that is equally applicable to children and adults, and that takes maximum advantage of the known relationships among IQ and genetic and environmental variance in intellectual development.