Measurement of Outcome
The measure of health outcome should be appropriate to the decision problem, should capture positive and negative effects on length of life and quality of life, and should be generalisable across disease states.
Importance to decision-making
It is important to use a measure of health outcome that is broad enough to capture all socially valued aspects of health and is applicable across investment types.
In scenarios where the scope of the decision problem is limited to interventions and comparators that impact either length of life or quality of life, it is still appropriate to use a measure that captures length and quality of life, as this allows proper consideration of the opportunity costs of investing in the intervention.
Using a non-disease specific health outcome measure (i.e. one that is generalisable across disease states) allows consideration of opportunity costs for the entire health sector, and facilitates comparisons across investment types. A disease-specific measure limits the ability of the decision-maker to make reasoned trade-offs between competing investments in different disease states, and can undermine comparability and consistency in decision-making.
The disability-adjusted life-years (DALYs) averted and the quality-adjusted life-years (QALYs) gained are measures that meet the requirements of the outcome principle in the iDSI Reference Case. The QALYs gained and the DALYs averted both provide a measure of quality and length of life, and are generalizable across different disease and therapeutic areas. Researchers will need to exercise judgment in choosing the most appropriate measure(s) for a given economic evaluation. Importantly, both the DALY and the QALY are based on a series of assumptions and simplifications that necessitates judgments about the appropriateness of the methods used to quantify health state preferences and the accuracy of the resultant measures. In addition, the use of DALYs and QALYs implicitly incorporates value judgments such as the additivity of health and ability to compare health across populations and conditions. Researchers should be aware of these judgments and assumptions when conducting and reporting analyses.
Depending on the scope of the decision problem however, the most appropriate outcome measure may sometimes be intervention- or disease-specific, and a generalizable outcome measure may be irrelevant or impractical to calculate. In all cases, a justification of the outcome measure chosen is required. Future iterations of the iDSI Reference Case will provide further guidance for researchers on the appropriate choice and calculation of an outcome measure. The fundamental consideration is that the choice of outcome measure is aligned to the needs of the intended decision maker and that the methods used to calculate the outcome measure are comprehensively and transparently described.