Causal indicators in quality of life research

Author(s): Hand, D. J., Bjordal, K., Groenvold, M.

Journal/Book: Qual Life Res. 1997; 6: 2-6 Boundary Row, London, England SE1 8NH. Rapid Science Publishers. 393-406.

Abstract: Quality of Life (QOL) questionnaires contain two different types of items. Some items, such as assessments of symptoms of disease, may be called causal indicators because the occurrence of these symptoms can cause a change in QOL. A severe state of even a single symptom may suffice to cause impairment of QOL, although a poor QOL need not necessarily imply that a patient suffers from all the symptoms. Other items, for example anxiety and depression, can be regarded as effect indicators which reflect the level of QOL. These indicators usually have a more uniform relationship with QOL, and therefore a patient with poor QOL is likely to have low scores on all effect indicators. In extreme cases it may seem intuitively obvious which items are causal and which are effect indicators, but often it is less clear. We propose a model which includes these two types of indicators and show that they behave in markedly different ways. Formal quantitative methods are developed for distinguishing them. We also discuss the impact of this distinction upon instrument validation and the design and analysis of summary subscales.

Note: Article Fayers PM, Norwegian Univ Sci & Technol, Med Teknisk Senter, Unit Epidemiol & Clin Res, Fac Med, N-7005 Trondheim, NORWAY

Keyword(s): quality of life instruments; construct validity; multi-item scales; composite scales; causal indicators; MODELS

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