For a number of years root cause analysis (RCA) has been used when an adverse event has occurred. It is generally accepted that adverse events do have causes, and that a careful analysis of the actions of persons and the states of the system in which the event occurred will reveal the causal agents. It remains only to select the most reasonable cause from the myriad of competing causes to bring the RCA to completion. RCA is obviously a reactive process taking place after the harm has been done.

Failure mode and effects analysis (FMEA) is less familiar to the medical world. It has little history in medicine although its military and industrial origins go back almost to World War II.¹ FMEA is a proactive process aimed at predicting the adverse outcomes of various human and machine failures, and system states.

FMEA and RCA cannot be separated. FMEA seeks to know the effects of each of all possible causal sets. RCA seeks to know the causal set of each of all possible effects. The underlying assumptions are that for every effect there must exist a set of causes (excluding the null set); and for every set of causes there must be some effect (including the null set). FMEA is the temporal mirror of RCA reflected in the “now” moment. FMEA looks forward in time; RCA looks backwards. …