Knight, Frederickson, and Martin's Self Perception Inventory can be of practical importance insofar as individuals contemplate themselves explicitly, but self is largely implicit, with feelings projected onto Q samples which are otherwise meaningless (the non-ens protopostulate). What is required is not merely orthogonal factors, but operant factors, i .e. , factors which make sense (schematical) and are subject to complementarity (ultimate, with no hidden variables). The principles involved are illustrated theoretically in terms of the selves of the priest in Thomas Hardy's In Church.
Operant Subjectivity

William Stephenson. (1987). Measurement of Self Perception: Some Reflection on the Article by Knight, Frederickson and Martin. Operant Subjectivity, 10(4), 125–135. doi:10.15133/j.os.1987.015