Salvage Therapy Trials in Invasive Fungal Disease: Challenges and Opportunities

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Abstract
The purpose of a clinical trial is to distinguish the effect of a medical intervention on clinical outcomes from the effect of other factors, such as the natural history of the disease or biased observations. The degree to which the causal relationship between the intervention and the outcome is free of extraneous influences is termed internal validity [1]. For a clinical trial to have internal validity, it should adhere to several well-accepted scientific principles. These include (1) a clear statement of the objective of the trial, (2) a meaningful, quantitative comparison with a control, (3) confirmation that the patient has the disease under study, (4) baseline comparability of patients at the start of the trial, (5) minimization of bias and confounding, (6) measurement of well-defined and reliable end points that reflect clinically meaningful outcomes important to patients, and (7) appropriate statistical analysis of trial results [2]. For a trial to provide results that one can extrapolate to clinical practice (i.e., for the trial to have external validity), it must adhere to these principles of internal validity.