Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The primary objectives of the current investigation were to: (a) examine the structure of subjective health risk perception in terms of some major variables (representativeness, availability, distress), hypothesized as influencing judgments of probability and severity of consequences; (b) determine the effects of anchoring (low, middle, high), referencing (self, other), and response format (frequency, analogue), conditions on the invariance of risk ratings; and (c) explore the degree to which personality factors (health concern, hypochondriasis), contribute to judgments of health risk. The stimuli used were 55 physical symptoms. A total of 500 subjects participated in this study. A threshold model of responding was used to decompose probability and severity judgments into threshold, salience and distance components for detailed analysis. LISREL modelling techniques were used in a double-cross validated study to determine the operating parameters relating components of probability and severity judgments to major cognitive, emotive and personality dimensions. Major results and conclusions of the study were: (a) A two component factor model of risk judgment was offered as an extension and refinement to models previously proposed in the literature; (b) The overriding dimensions contributing to judgments of risk appear to be distress and perceived controllability; (c) Both optimistic and pessimistic biases in probability and severity judgments were observed depending on the referencing context. These biases tended to decrease as familiarity of the symptoms increased; (d) Anchoring manipulations affected individuals' judgments of probability, but did not influence judgments of severity: Referencing manupulations affected judgments of severity but did not influence judgments of probability; (e) LISREL results indicated some support for the model proposed by Kahneman and Tversky, for data where the aggregation is over stimuli. The use of a two component threshold model to break judgments down into psychometric components revealed relationships between variables, otherwise missed by more molar approaches; and (f) Personality dimensions had both direct and indirect influences on probability judgments (but not on severity judgments) under self-referenced conditions.



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