Abstract
This chapter reviews methods used to measure comorbidity in the context of cancer; summarising methods, identifying contexts in which they have been used and assessing the validity, reliability and feasibility of each approach. Measures of comorbidity are categorised according to whether they are based on individual conditions or simple counts, on dysfunction/function of organ systems, on conditions that have been weighted and combined into indices or based on alternative approaches. Twenty-one separate approaches are described. Content and face validity of the measures varied but tended to be higher for those developed for cancer populations. Some evidence supporting criterion validity of all approaches was found. Where reported, reliability tended to be moderate to high. Some approaches tended to score well on all aspects, but were resource intensive in terms of data collection. There is no gold standard approach to measuring comorbidity in the context of cancer. All summary approaches require simplifying assumptions and, by necessity, result in loss of information. Approaches vary in their strengths and weaknesses, with the choice of measure depending on the study question, population studied and data available.