This Technical Support Document (TSD) is concerned with methods for identifying and reviewing evidence to inform models developed to estimate the cost-effectiveness of health technologies, in particular model parameter estimates, in the NICE Technology Appraisal Process. The NICE Guide to the Methods of Appraisal states that for parameters relating to treatment effects a full systematic review is required, and that the process of assembling evidence for all parameters needs to be systematic, transparent and justifiable. Evidence must be identified, quality assessed and, when appropriate, pooled using explicit criteria and justifiable and reproducible methods. The Methods Guide goes on to state that evidence will typically be drawn from a number of different sources. These sources might include cohort studies for parameters relating to the natural history of the condition, randomised controlled trials for relative treatment effects, and cross-sectional surveys for resource use and costs. Methodological standards for reviewing the broad range of relevant evidence in the context of model development do not currently exist. The processes through which evidence is identified and selected remain largely unreported with the result that the process of using evidence within models lacks transparency. Guidance is needed regarding approaches for reviewing of evidence to inform the model development process and for informing parameter values in cost-effectiveness models.

The purpose of this document is to provide guidance and advice on what might constitute a systematic and transparent approach where there is not a requirement to use conventional systematic review methods but where little procedural guidance exists. The document covers four key objectives:

• To recommend model structuring methods including the identification and specification of relevant parameters within a model.
• To recommend appropriate methods for the systematic identification of evidence to inform model parameter estimates including relevant sources and types of searching.
• To recommend appropriate methods for the reviewing of evidence to inform model parameters in a systematic fashion including recommendations for critical appraisal and rapid review methods.
• To make recommendations on the reporting of the identification and reviewing of evidence including methods, decisions and judgements made during the process.

The guidance presented within this TSD is not intended to be prescriptive, rather the intention is to provide practical advice on how specific methods might be implemented. This support guide is set out across four sections: (1) model structuring; (2) identifying the evidence; (3) reviewing the evidence; and (4) recommendations for practice.