No abstract

Doubt is raised that revolutions in measurement theory, for example conjoint measurement or Rasch measurement, will lead to the quantification of psychological attributes. First, the meaning of measurement is explained. Relying on this, it is demonstrated that in order to attain quantification under causally complex circumstances it is necessary to manipulate the phenomena involved and control systematic disturbances. The construction of experimental apparatus is necessary to accomplish these tasks. The creation of modern quantitative science through the adoption of this method is called the Galilean revolution. Next the Millean quantity objection is formulated. If the Galilean revolution is not possible in psychology, the task of quantification is not solvable. The objection is defended. Psychological phenomena are neither manipulable nor controllable to the required extent. Therefore they are not measurable.

The prevalence of depressive symptoms in the general population and at the prodromal stage of numerous mental disorders precipitated by various psychological and biological factors suggests that depression might be an expression of an inborn mild reaction pattern of the human brain. With progressing brain dysfunction more severe patterns like psychosis are expressed.

According to classical measurement theory, fundamental measurement necessarily requires the operation of concatenation qua physical addition. Quantities which do not allow this operation are measurable only indirectly by means of derived measurement. Since only extensive quantities sustain the operation of physical addition, measurement in psychology has been considered problematic. In contrast, the theory of conjoint measurement, as developed in representational measurement theory, proposes that the operation of ordering is sufficient for establishing fundamental measurement. The validity of this view is questioned. The misconception about the advantages of conjoint measurement, it is argued, results from the failure to notice that magnitudes of derived quantities cannot be determined directly, i.e., without the help of associated quantitative indicators. This takes away the advantages conjoint measurement has over derived measurement, making it practically useless.

The Millean Quantity Objection—that is, the claim that the measurement of psychological attributes is impossible (Trendler, 2009)—has been countered with partly vigorous opposition (Kyngdon, 2013; Markus & Borsboom, 2012; Saint-Mont, 2012). Kyngdon’s response is of particular interest, since he asserts that measurement may already have been established. If correct, it would definitely invalidate any quantity objection and end the century-long discussion about the measurability of psychological attributes. Therefore the focus of the rejoinder will be on the question of when measurement is reached. First the meaning of measurement is elaborated. On this basis, criteria for the successful establishment of measurement are formulated and it is outlined how these are satisfied in the case of intensive quantities. It is concluded that the evidence presented by Kyngdon is insufficient and inadequate. The approach will also serve as background to discuss objections raised against the Millean Quantity Objection.