The illusion of certainty - a deluded perception?

BACKGROUND: Certainty is seen as the 'Holy Grail' of science, despite the fact that all science is based in doubt, and that good scientists always leave a door open for an alternative explanation of their findings. Certainty also is a human desire providing comfort and surety. How can these two notions coexist? RESULTS: The way we perceive is the way we see and understand. Perception, however, is not objective; the way we 'know' what the sensory input we receive means arises from matching it against stored images of prior experiences, or put differently, the way we perceive the world depends on successfully predicting our own sensory status. Only large mismatches create new awareness resulting in new learning. At large we are prisoners of our own making, and awareness of the boundaries of our understanding will help to expand our horizon. DISCUSSION AND CONCLUSIONS: The four papers of this edition attempt to expand the boundaries of 'common certainty' in terms of statistical interpretation, management of individual patients, disease management and health policy.