Choosing a Time Horizon in Cost and Cost-effectiveness Analyses

INTRODUCTION

This JAMA Guide to Statistics and Methods reviews considerations that go into investigators’ choice of time over which to define and measure the benefits and costs of interventions in risk-benefit and cost-effectiveness analyses.

When designing a comparative outcomes or a cost-effectiveness analysis, the time horizon defining the duration of time for outcomes assessment must be carefully considered. The time horizon must be long enough to capture the intended and unintended benefits and harms of the intervention(s).^1,2 In some instances, the time horizon should extend beyond the duration of a clinical trial when a specific end point is measured, whereas in other instances modeling outcomes over a longer period is unnecessary. Using a longer time horizon than is necessary may add unnecessary cost and complexity to the cost-effectiveness analysis model.

In a study published in JAMA Ophthalmology, Wittenborn et al³ examined costs and effectiveness of home-based macular degeneration monitoring systems using a lifetime horizon in a cost-effectiveness analysis and a 10-year horizon in a budget impact analysis. The rationale for selection of time horizons and their implications for interpreting the research is reviewed in this JAMA Guide to Statistics and Methods article.

THE USE OF TIME HORIZON IN A COST-EFFECTIVENESS ANALYSIS

For cost-effectiveness, the time horizon is the time over which the costs and effects are measured.^1,2 Cost-effectiveness analyses should consider time horizons that capture all intended and unintended consequences of the interventions being evaluated, irrespective of when they occur. When a cost-effectiveness analysis is performed as part of a clinical trial, the time in which the data are collected may be limited to the duration of the trial itself. This is called a within-trial horizon.⁴ For example, cost-effectiveness of antibiotics used to treat acute sinusitis can use a within-trial time horizon because the disease and its treatment occur over a very short period and extrapolation of benefits over a long period is not required.

If benefits and harms of an intervention can occur over the entirety of a patient’s life, then a lifetime horizon is appropriate. For example, cost-effectiveness for the use of a low vs a high dose of aspirin may affect the primary end point of cardiovascular events within the trial period, but the effects are likely to continue throughout the patients’ lifetime. In such cases, within-trial analyses based on the primary end point are incomplete and potentially misleading because the long-term population effects on health and costs and results would not be captured.⁵ In some instances, the appropriate time horizon can be somewhere between the duration of the trial and the lifetime of patients; eg, when a cost-effectiveness analysis is conducted from a payer’s perspective. However, choice of time horizon can have substantial influence on cost-effectiveness analysis results in such cases.⁶

LIMITATIONS REGARDING SELECTION OF TIME HORIZONS

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