Cost-Effectiveness and Heterogeneity: Using Finite Mixtures of Disease Activity Models to Identify and Analyze Phenotypes

Heterogeneity in patient populations is an important issue in health economic evaluations, as the cost-effectiveness of an intervention can vary between patient subgroups, and an intervention which is not cost-effective in the overall population may be cost-effective in particular subgroups. Identifying such subgroups is of interest in the allocation of healthcare resources. Our aim was to develop a method for cost-effectiveness analysis in heterogeneous chronic diseases, by identifying subgroups (phenotypes) directly relevant to the cost-effectiveness of an intervention, and by enabling cost-effectiveness analyses of the intervention in each of these phenotypes. We identified phenotypes based on healthcare resource utilization, using finite mixtures of underlying disease activity models: first, an explicit disease activity model, and secondly, a model of aggregated disease activity. They differed with regards to time-dependence, level of detail, and what interventions they could evaluate. We used them for cost-effectiveness analyses of two hypothetical interventions. Allowing for different phenotypes improved model fit, and was a key step towards dealing with heterogeneity. The cost-effectiveness of the interventions varied substantially between phenotypes. Using underlying disease activity models for identifying phenotypes as well as cost-effectiveness analysis appears both feasible and useful in that they guide the decision to introduce an intervention

Nongastrointestinal disorders in the irritable bowel syndrome

A large proportion of irritable bowel syndrome (IBS) patients also complain of other functional disorders, such as headache, noncardiac chest pain, low back pain, and dysuria. Some of these features, particularly headache, may have a negative influence on the outcome of IBS. In a large proportion of female IBS patients, sexual intercourse triggers the symptoms, and frequently IBS symptoms exacerbate during menses. These gynecological-type symptoms often mislead the patients to the gynecological clinic, which may imply unnecessary investigations and inappropriate treatments. The diagnostic criteria of the fibromyalgia syndrome include IBS, and hence, the apparent relationship of both syndromes is difficult to analyze. On the other hand, no convincing evidence has been produced to date to sustain an association between IBS and the chronic fatigue syndrome