Krefting (1985) suggests that for occupational therapy conceptual models attempt to answer the questions: what do therapists evaluate and treat, and why? Building conceptual models to answer these questions is viewed as an evolutionary process which begins with an idea (Reynolds, 1980). The process moves from idea to conceptualisation and involves a classification system in which a guiding set of concepts is developed. Finally, the conceptualisation evolves into relational statements that can be evaluated by agreement and inter-subjectivity of the professional community involved (Reynolds, 1980; Yerxa, 1983). The Occupational Performance Model (Australia) outlined in this article represents an example of the stage of model building where concepts have been developed, classified and related, but not yet fully evaluated or tested.

Dichoff, James and Wiedenback (1968) describe four developmental levels in model building that occur in practice disciplines such as occupational therapy. The most rudimentary level is “factor isolating”, wherein terminology is developed (1968, p.416). The second level is referred to as, “factor relating” whereby suggestions are made as to how concepts are interrelated. The third level includes, “situation relating” which identifies how the model is able to make predictions and specify the nature of the relationship. A “situation producing” model is a product of the fourth level and allows the model to be used prescriptively.

The Occupational Performance Model (Australia) has some characteristics of all the levels of model building outlined. Constructs in the model are named and defined (factor isolating); interactions between constructs are suggested (factor relating); propositions are made as to the association relationship which exists between constructs (situation relating); and the model can be used to establish goals and determine action or non-action (situation producing).

Concepts are the building blocks of conceptual models and can be identified as concrete, behavioural or abstract (Krefting 1985). The key concepts defined within each level of the model can be viewed as abstract and symbolic in nature and, therefore, are more correctly described as constructs. Relationships between constructs are referred to as principles (Payton, 1979). Relationships in this occupational performance model are depicted by arrows between constructs, and provide the hypothesised rules for action and future direction for research to verify the model.