Since its introduction into medicine 15 years ago, decision analysis has been applied to difficult clinical problems. Several important advances have made the process more practical and acceptable: computer programs that eliminate the need for burdensome calculations, improved techniques for designing analytic models, the ability to carry out sensitivity analyses over several dimensions simultaneously, and the elaboration of clinically relevant measures of utility. Using these techniques, analysts have addressed many important clinical issues including screening for and prevention of disease, tradeoffs among tests and treatments, and the interpretation of clinical data under conditions of uncertainty. Problems with the approach remain and applications have not been extensive, but decision analysis is evolving as a powerful clinical tool and gradually is gaining acceptance in medical practice.

We used decision analysis to compare the conventional strategy of biopsy-tailored therapy with alternative strategies not using renal biopsy in treating adults with idiopathic nephrotic syndrome. We evaluated data on steroid and platelet-inhibitor therapies and a new clinical strategy, empiric sequential therapy. This sequential approach involves use of short-term alternate-day steroid agents, followed by long-term platelet inhibitors for persistent nephrotic syndrome. Our results indicate that, contrary to usual practice, use of renal biopsy is not necessary in caring for adult patients with idiopathic nephrotic syndrome; empiric short-term alternate-day steroid therapy is equally efficacious. If the benefits of platelet-inhibitor therapy for treating membranoproliferative glomerulonephritis are confirmed, empiric sequential therapy also will be equally efficacious. Our study shows how decision analysis can be used to identify superfluous diagnostic procedures.

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Standard‐of‐care HIV pre‐exposure prophylaxis (PrEP) is highly efficacious, but uptake of and persistence on a daily oral pill is low in many settings. Evaluation of alternate PrEP products will require innovation to avoid the unpractically large sample sizes in noninferiority trials. We propose estimating HIV incidence in people not on PrEP as an external counterfactual to which on‐PrEP incidence in trial subjects can be compared. HIV recent infection testing algorithms (RITAs), such as the limiting antigen avidity assay plus viral load used on specimens from untreated HIV positive people identified during screening, is one possible approach. Its feasibility is partly dependent on the sample size needed to ensure adequate power, which is impacted by RITA performance, the number of recent infections identified, the expected efficacy of the intervention, and other factors. Screening sample sizes to support detection of an 80% reduction in incidence for 3 key populations are more modest, and comparable to the number of participants in recent phase III PrEP trials. Sample sizes would be significantly larger in populations with lower incidence, where the false recency rate is higher or if PrEP efficacy is expected to be lower. Our proposed counterfactual approach appears to be feasible, offers high statistical power, and is nearly contemporaneous with the on‐PrEP population. It will be important to monitor the performance of this approach during new product development for HIV prevention. If successful, it could be a model for preventive HIV vaccines and prevention of other infectious diseases.

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