Identification of evidence for key parameters for health economic models used to evaluate the cost-effectiveness of health care technologies

Objectives. The objective of this PhD study was to compare different information retrieval methods that can be used to identify health economic model inputs. Methods. Existing search methods were compared to two alternatives (iterative searching and rapid review), using three health technology assessment (HTA) case studies in ulcerative colitis, thyroid cancer and breast cancer tumour profiling risk stratification. Key criteria for selecting the case studies were the availability of an executable Excel model. Two model inputs were chosen to be tested: health state utilities and baseline risk of clinical events. Usual practice searches were updated, and alternative search methods (iterative searching and rapid review) were conducted, and the differences in model inputs identified by each search approach were analysed. Differences were evaluated in terms of time taken to search, sensitivity, burden (precision and number needed to read) and relevance of identified information. The identified model input values were tested in an executable health economic model, and, when feasible, the model results were compared in order to understand the impact on model outputs. Results. Usual practice for identifying health state utility inputs was a systematic review in all except one case study, where a previous health economic model output was used. In all case studies the alternative search methods were mostly less resource intensive and resulted in identical or similar model inputs, with no changes to the conclusions drawn from the health economic model. Usual practice for identifying baseline risk of clinical events varied from no recorded search steps to a systematic review. When the effort for usual practice could not be estimated due to the lack of recorded search steps, the time difference could not be estimated. However, it was clear that applying alternative search methods increased the transparency. Conclusions. Alternative search methods were more efficient and more transparent than established search methods, without impacting the health economic model conclusions. Further case studies are required to examine whether this conclusion remains generalisable, and applies to other health economic model inputs.