The consumption of alcohol appeared to eliminate the strong associations found in placebo group between individual difference measures and persistence. The analogue game was accepted by participants as a valid form of gambling. The result showed that relatively small quantities of alcohol have a significant effect on the psychological processes that underpin self-control over gambling. This finding challenges the conceptual research paradigm of studying co-morbidity or dual-addicted clinical populations as the most appropriate method of understanding how two addictive behaviours interact.

Representational measurement theory is the dominant theory of measurement within the philosophy of science; and the area in which the theory of conjoint measurement was developed. For many years it has been argued the Rasch model is conjoint measurement by several psychometricians. This paper critiques this argument from the perspective of representational measurement theory. It concludes that the Rasch model is not conjoint measurement as the model does not demonstrate the existence of a representation theorem between an empirical relational structure and a numerical relational structure. Psychologists seriously interested in investigating traits for quantitative structure should use the theory of conjoint measurement itself rather than the Rasch model. This is not to say, however, that empirical relationships between conjoint measurement and the Rasch model are precluded. The paper concludes by suggesting some relevant research avenues.

Psychometricians hypothesize that cognitive abilities such as reading, writing and spelling are measurable. However, they prefer to model item response probabilities than to study the internal structure of cognitive attributes. The theory of conjoint measurement, via its unique capacity to detect the quantitative structure of non-extensive attributes, can be used for the latter purpose. It is shown that conjoint systems analogous to the numerical composition rules advanced by the Rasch, many facet Rasch and two-parameter logistic models can be formulated using well-established axioms, representation theorems and proofs. Examples using empirical and synthetic data are presented. It was concluded that the lack of descriptive, behavioural theory remains the biggest obstacle to the scientific measurement of cognitive abilities.

Trendler (2009) argued that psychological attributes cannot be measured, as the experimental manipulation and control necessary for the application of measurement theory cannot be achieved. It is argued that Trendler's conclusion ignored deeper issues. The scientific measurement of psychological attributes depends not only upon adequate stimulus control, but also upon descriptive theories of psychological systems and the demonstration of pure differences in degree (magnitude) within attributes hypothesized to be quantitative. For some classes of stimuli, where descriptive theories of the response process exist and where quantitative features in the stimuli themselves can be empirically manipulated, the demonstration of pure differences in degree is plausible and the scientific measurement of the relevant attributes credible. Where attribute differences between stimuli have identified qualitative causes, stimuli cannot be engineered to produce equivalent magnitudes of the relevant attribute. Here is where Trendler's Millean Quantity Objection has force.

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