Will COVID-19 be evidence-based medicine’s nemesis?

10 July, 2020

Below are the citation and selected extracts from an editorial in PLoS Medicine. Full text here: https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1...

CITATION: Will COVID-19 be evidence-based medicine’s nemesis?

Trisha Greenhalgh

PLoS Medicine

Published: June 30, 2020 https://doi.org/10.1371/journal.pmed.1003266


Once defined in rhetorical but ultimately meaningless terms as “the conscientious, judicious and explicit use of current best evidence in making decisions about the care of individual patients” [1], evidence-based medicine rests on certain philosophical assumptions...

The trouble with pandemics is that these assumptions rarely hold...

It is surely time to turn to a more fit-for-purpose scientific paradigm. Complex adaptive systems theory proposes that precise quantification of particular cause-effect relationships is both impossible (because such relationships are not constant and cannot be meaningfully isolated) and unnecessary (because what matters is what emerges in a particular real-world situation)... The 20th-century logic of evidence-based medicine, in which scientists pursued the goals of certainty, predictability and linear causality, remains useful in some circumstances (for example, the drug and vaccine trials referred to above). But at a population and system level, we need to embrace 21st-century epistemology and methods to study how best to cope with uncertainty, unpredictability and non-linear causality [16].

In a complex system, the question driving scientific inquiry is not “what is the effect size and is it statistically significant once other variables have been controlled for?” but “does this intervention contribute, along with other factors, to a desirable outcome?”. Multiple interventions might each contribute to an overall beneficial effect...

Whilst it is hard to predict anything in real time, history will one day tell us whether adherence to “evidence-based practice” helped or hindered the public health response to Covid-19—or whether an apparent slackening of standards to accommodate “practice-based evidence” was ultimately a more effective strategy.


While not an expert, my sense is that evidence-based medicine (and systematic reviews) have contributed enormously to policy and practice, but they are not a panacea. I know less about 'complex adaptive systems theory'. I suspect there is a role for both, and sometimes the two will sit uncomfortably side by side in relation to the same issue. What do you think?

Best wishes, Neil

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HIFA profile: Neil Pakenham-Walsh is coordinator of the HIFA global health campaign (Healthcare Information For All - www.hifa.org ), a global community with more than 20,000 members in 180 countries, interacting on six global forums in four languages in collaboration with WHO. Twitter: @hifa_org FB: facebook.com/HIFAdotORG neil@hifa.org