TITLE PROJECT Comparison of modern psychometric models for analyzing the structure and the validity of psychological questionnaire data PROJECT DESCRIPTION: Constructs such as anxiety, depression, quality of life, pain, mood, affectivity, and fatigue often lack support by a well-established theory that explains their structure, underlying processes and relationships with other constructs; such theory often is absent or primitive at best. Multi-item questionnaires that purport to measure a particular construct are often validated using rather vague, ad hoc methods based on rather imprecise notions such as internal consistency (items are positively associated), convergent validity (questionnaires measuring the same or related constructs correlate rather highly) and divergent validity (questionnaires measuring different constructs correlate rather lowly).