State-trace analysis: A method of testing simple theories of causation

An independent variable measures some aspect of a treatment applied to a person; a dependent variable measures some aspect of the treatment's effect upon the person. Two dependent variables will often covary with each other because they are affected by a common independent variable. A state trace is a graph which plots the value of one dependent variable as a function of another. (Thus, a state trace is a generalization of the yes-no receiver-operating-characteristic curve.) By appropriately analyzing state traces, it is possible to test theories concerning (a) the mechanisms by which independent variables affect dependent variables and (b) how these mechanisms differ from one population of persons to another. As an illustration, a study of long-term memory in normal persons, schizophrenics, and persons with organic brain syndrome is presented. The effects of number of word presentations and length of retention interval upon probability of word recall and recognition were investigated. The results were analyzed by state-trace analysis.