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There is no evidence to suggest

post-clear-languageThe six most dangerous words in evidence-based medicine (EBM) do not directly cause deaths or adverse events. They do not directly cause medical errors or diminutions in quality of care. However, they may indirectly cause these adverse consequences by leading to false inferences for decision making. Consider the following statements, each of which includes the six most dangerous words:

  • There is no evidence to suggest that hospitalizing compared with not hospitalizing patients with acute shortness of breath reduces mortality.
  • There is no evidence to suggest that ambulances compared to taxis to transport people with acute GI bleeds reduces prehospital deaths.
  • There is no evidence to suggest that looking both ways before crossing a street compared to not looking both ways reduces pedestrian fatalities.

All of these statements are clearly absurd as foundations for decision making, yet they are technically correct. In each case, these hypotheses have been untested and therefore there is no evidence to suggest otherwise, presuming a definition of “evidence” that requires formal hypothesis testing in an adequately powered study.1 Indeed, as of this writing, “there is no evidence to suggest” appears in MEDLINE 3055 times, nearly as often as “decision analysis” (3140 times), a common framework for using evidence to make decisions. My anecdotal experience suggests that “there is no evidence to suggest” is a mantra for EBM practitioners, in a wide variety of settings. And it is infrequently followed by the clarifying aphorism “absence of evidence is not evidence of absence”2 or discussions of more inclusive definitions of “evidence.”3,4

Deciding not to intervene when “there is no evidence to suggest” the favorability of an intervention makes sense from a decision analytic perspective when the act involves potential harm or large resource commitments.5 However, deciding to intervene when “there is no evidence to suggest” also may make sense, particularly if the intervention does not involve harm or large resource commitments, and especially if benefit is suggested by subjective experience (eg, the qualitative analogue of the Bayesian prior probability).6

Indeed, the fundamental problem with the phrase “there is no evidence to suggest” is that it is ambiguous while seeming precise. For example, it does not distinguish between the vastly different evidentiary bases of US Preventive Services Task Force (USPSTF) grades I, D, or C, each of which may have distinct implications for decision making.7There is no evidence to suggest” may mean “this has been proven to have no benefit” (corresponding to USPSTF grade D), which has very different implications than alternative meanings for “there is no evidence to suggest” such as “scientific evidence is inconclusive or insufficient” (corresponding to USPSTF grade I) or “this is a close call, with risks exceeding benefits for some patients but not for others” (corresponding to USPSTF grade C). As a result, these six dangerous words may mask the uncertainty of experts. They even may be used to deny treatments with potential benefit, if they are interpreted as the equivalent of USPSTF grade D (“this has been proven to have no benefit”) but really mean the equivalent of USPSTF grade I (“scientific evidence is inconclusive or insufficient”).


Click here to read more from this article by R. Scott Braithwaite (originally titled “EBM’s Six Dangerous Words”) from the November 27, 2013 edition of Journal of the American Medical Association.

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