Measuring subjective health outcomes : methodological and theoretical considerations

• Main Author: Pollard, Beth
• Published: University of Aberdeen 2007
• Subjects: 610.21
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485381

This thesis examines methodological and theoretical issues related to health outcome measures. The International Classification of Functioning, Disability and Health (ICF) has become widely adopted as the theoretical framework of choice. The evaluation and assessment of any theoretical model depends on appropriate measures. It is important to establish that each measure is assessing only the theoretical construct of interest and not other constructs; otherwise, observed relationships between constructs may be misleading. It was shown that existing osteoarthritis measures and items were contaminated with other ICF constructs based on classifications by expert judges. However, a pool of uncontaminated items was identified by the expert judges. These items formed the basis of new measures of Impairment (I), Activity Limitation (A) and Participation Restriction (P). The items were examined using responses from patients having a hip or knee replacement. Item analysis was carried out combining item response theory and classical test theory methods, and led to the removal of misfitting items. Using all the uncontaminated items, patients' responses to the items did not result in statistically separable measures. However, statistically independent I, A and P measures were established using a reduced item set, and these measures appeared to provide a more accurate estimation of the ICF pathways than pre-existing measures. Overall, this thesis highlights the importance of developing health outcome measures that are theoretically-based and both uncontaminated and statistically independent.