The Association for the Accreditation of Human Research Protection Programs (AAHRPP) notes that of the organizations it surveyed (it doesn't report how many or how they were selected) 63 percent "did not disapprove any protocols in the past year" and only "13.2 percent disapproved two or more percent." The AAHRPP uses these figures to argue that the "perception that IRBs disapprove a significant portion of research protocols submitted is not true."
I wonder whom they are accusing of holding this perception. Serious observers of IRBs know that a board need not formally reject a proposal to make it impossible for the researcher to proceed. Look at what happened at Linda Thornton. Look at what happened to Kathryn Edgerton-Tarpley's student. Or the anonymous researcher who wanted to study how parents discipline their children. In these cases, researchers abandoned projects in the face of IRB intransigence, allowing the IRB to claim it had not disapproved the project.
I am therefore unsurprised by AAHRPP's figures. I am surprised that AAHRPP thinks that formal disapproval is a meaningful measure of the IRB suppression of research, and by its stooping to this straw man argument.