Case Formulation

Introduction

One of the principal aims of a psychological assessment is to evaluate the form and function of target behaviours. The term case formulation can be defined as the process of operationalizing target behaviours1 (determining the form) and evaluating relationships among target behaviours and potential controlling factors (determining the function) for an individual client.

The aforementioned definition has several important features. First, the identification of causal functional relationships is a central element of case formulation. Although functional relationships may be either correlational or causal, by itself, a functional relationship implies only covariation [Page 165]between two variables. Because a case formulation is primarily used in treatment planning, the identification and quantification of causal functional relationships among target behaviours and controlling factors are of primary interest.

Causal functional relationships are best thought of as elevated conditional probabilities (James, Mulaik & Brett, 1982), wherein the probability of observing a change in the form of a target behaviour (change in frequency, intensity, duration of response), given the occurrence of a hypothesized causal event (the conditional probability of the target behaviour), is greater than the probability of observing a change in the form of a target behaviour without the prior occurrence of the hypothesized causal event (the base rate or unconditional probability of the target behaviour). To illustrate, let A equal an increase in the frequency of worry experienced by a middle-aged client (the target behaviour), let B equal an increase in work stress (hypothesized causal event), and let P equal the probability. A tentative causal functional relationship between worry and work stress would be inferred if the probability of the frequency of worry after an increase in work stress [P(A|B)] was greater than the base rate probability of worry [P(A)].

Many internal and situational events may be causally associated with a target behaviour. For example, changes in central nervous system neurotransmitter levels, loss of response-contingent reinforcement, increased levels of family conflict, negative expectations, and seasonal changes may all exert causal influences on depressed mood for a particular client. Although several causal relationships may exist, in designing an intervention, we are most interested in the subset of causal relationships that exert significant causal effects on a target behaviour. Therefore, a second characteristic of case formulation is a focus on the identification of important causal functional relationships.

However, important causal functional relationships are often uncontrollable. For instance, two sets of potentially important causal factors that cannot be controlled or modified include significant historical events, such as exposure to trauma or economic changes, and biological attributes, such as genetic predisposition. Because interventions are designed to elicit change in target behaviours by modifying potential causes, a third characteristic of case formulation is an emphasis on current and controllable causal functional relationships.

In addition, a fourth characteristic of case formulation is its idiographic focus. Specifically, case formulations are typically designed to identify causal functional relationships applicable to a specific set of target behaviours for an individual client. This idiographic approach is consistent with the notion that important between-person differences exist in the causes of behaviour and that interventions should be individually tailored in order to maximize effectiveness.

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