Last week the New England Journal of Medicine (NEJM) published a paper on selective outcome reporting in clinical trials (Vedula et al. 2009). The primary and secondary outcome(s) of a clinical trial could for example be survival in cancer patients or rate of heart attacks and other cardiovascular events in patients taking cholesterol-lowering drugs. These outcomes are defined in the study protocol before the first patient is treated, and whether or not the primary outcome is reached (using statistical testing) defines whether a trial was positive or negative. The study protocol is approved by an institutional review board (IRB) and can only be changed later (and that includes changes in the protocol-defined outcomes) if again approved by the IRB.
This is a companion discussion topic for the original entry at https://front-matter.io/mfenner/publication-bias-in-clinical-trials