Why evidence cannot replace opinion

One of the key principles of evidence-based practice is that health care decisions are informed by the best available research evidence. However, many people assume that once the best ‘truth’ is known and described in terms of the research evidence, we will all just change our behaviour accordingly; that is patients and clinicians… While we can describe the unidirectional cause and effect of certain drugs on human physiology, we cannot reduce the complexities of individual behaviour or the way social communities function to such simple one-way causal predictions. Knowing the evidence is not enough to change behaviour. Individual experience and opinion has an important part to play as well.

If we think about the nature of knowledge, we might like to look for the real truths and assume that if we use the best scientific methods and reduce all possible sources of bias, we can get very close to what is true and real. This epistemological perspective of positive realism or positivism has often been interpreted as the source of evidence-based practice. Over the last 20 years, there has been a dramatic understanding of the benefits of using different research methodologies. We have built and codified a massive knowledge base about how and why many drugs and healthcare interventions work.

However, at the same time, there has been an increasing recognition that we all have different experiences, and are influenced by specific cultural or organisational interpretations to create our own meaning and opinions, which inevitably influence future behaviours and decisions. This epistemology of constructivism is helpful in explaining why some people do not adopt what others might think is the best evidence for them. By understanding that people are influenced by their local culture, organisations and experiences, we can begin to understand why we all don’t just adopt new research evidence automatically.

Perhaps the solution lies in adopting a pragmatic perspective that recognises a middle path  where competing positivist and constructivist world views can be recognised and integrated in some way to gain a more complete and complementary understanding. Neither is right or wrong, but both can help explain different aspects. Perhaps we can respect both the contributions and limitations of scientific research evidence, at the same time that we recognise the importance of personal experience and opinion and the range of different perspectives of individuals and groups. Years of research in psychology and sociological traditions have validated this individual variability – but rather than this being totally chaotic and random, there are some explanatory patterns. We need to expand the study of research methodologies to better understand both the content and processes of behaviour change at individual, group and organisational levels. We need to use transparent, systematic and scientific principles to describe and distinguish between the creation, dissemination and implementation of research evidence.

Evidence alone is rarely ever sufficient in making a decision. Individual experiences will always be unique and this will be the source of a variety of tacit beliefs. Rather than ignore these as unpredictable and idiosyncratic opinions, we need to find ways of critically and transparently integrating the individual experiences of both healthcare practitioners and patients with the large body of well organised research evidence.


I conduct and supervise research that promotes the translation of quality research evidence for use in clinical practice.

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Posted in behaviour, change, evidence, implementation, opinion
One comment on “Why evidence cannot replace opinion
  1. […] Why evidence cannot replace opinion (knowledgetranslationoxfordblog.wordpress.com) […]

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