There are multiple challenges in conducting economic evaluations including the time frame chosen and statistical power.

Time Horizon

The time horizon of the analysis is determined when defining the perspective, and represents how far out into the future costs and benefits should be evaluated. The appropriate time horizon depends on the clinical problem. Interventions designed for acute problems may not require long-term time horizons. In contrast, economic evaluations of interventions for chronic conditions will require longer time horizons. Importantly, the time period chosen should not produce misleading results. Several studies have shown that over short periods of time there may be differences in costs; however, over time, cost differences may disappear (Drummond et al., 2005; Gold et al., 1996). Practically, the time horizon generally corresponds to the length of time for which data are available. For example, studies using participant-level data collected in randomized trials will generally have shorter time horizons than studies using data from long-term cohort studies. However, decision analytic methods (e.g., Markov models) can be combined with participant-level data to extrapolate beyond the data (Briggs et al., 2006; Hunink & Glasziou, 2001). Extrapolating beyond the data is important when it is believed that there are important long-term outcomes associated with the intervention and there are only short-term data available.

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