Measurement in psychology: A case ofignoramus et ignorabimus? A rejoinder

Abstract

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.