Hans-Peter Krüger

• The methodological implications of a differential psychopharmacology are discussed. It is shown that the technique of stratifying subjects with personality scores depends on one basic assumption: the personality score is not affected by the other experimental factors. Two experiments are reported in which pre- and posttest (after the experiment) scores were measured. The pre-post-differences showed themselves to be affected by the medication. It is argued that in psychopharmacological experimentation an additional step must be included. AllThe methodological implications of a differential psychopharmacology are discussed. It is shown that the technique of stratifying subjects with personality scores depends on one basic assumption: the personality score is not affected by the other experimental factors. Two experiments are reported in which pre- and posttest (after the experiment) scores were measured. The pre-post-differences showed themselves to be affected by the medication. It is argued that in psychopharmacological experimentation an additional step must be included. All non-treatment factors must be examined for their stability in the course of the experiment. If they are stable, usual evaluation may take place. If changes are attributable to the treatment, personality scores must be regarded as dependent variables. They have to be evaluated together with the other observables with a multivariate model. Additionally, a procedure like this yields as "experimental differential psychology" a self-reliant contribution to the problems of differential psychology.…