• Plausible biological mechanisms, that is, the ability to fit the observed relationships into some larger body of theory and evidence on how the body works.

• Consistency of findings from study to study. A single study is rarely definitive, although some large, well-designed clinical trials may produce evidence that is treated by the scientific community as definitive. Confidence in the existence of cause-and-effect relationships grows with the ability to see them in multiple studies over time. Confidence diminishes when results vary from study to study.

• Dose-response relationships. In most biological processes, the introduction of a larger amount of a substance produces a larger subsequent effect. There is almost always some upper limit at which no further effect is found or some different or counterbalancing biological process begins to take over. For the most part, however, within a reasonable range of doses, more “cause” produces more “effect.” Clear dose-response relationships typically increase the confidence in the underlying causal relationships between the treatment and the outcome.

Medical school, nursing school, and allied health school faculty require evidence of treatment effectiveness to determine how to train students. The standards of evidence for specific treatments are not necessarily the same as those used by researchers, but they are similar. They include

• The criteria for researchers listed above. Faculty have the responsibility to stay current with the published literature and generally to apply the same criteria to published studies that researchers apply.

• Personal experience. In addition, however, clinical faculty draw heavily on their own experiences in determining which treatments are effective and which ones are not. This may be particularly true in the context of