Objectives In Britain, GPs are responsible for prescribing multiple long-term treatments to their patients. To support shared clinical decision making, understanding of the absolute benefits and harms of individual treatments is needed. International evidence shows that doctors’ knowledge of absolute treatment effects is poor, but this has not been researched among British GPs.

Aim To assess and describe the level and range of the quantitative understanding of the benefits and harms of treatments for common long-term conditions among British GPs.

Method An online survey distributed to GPs in Britain over two months in 2018. Participants were asked to estimate the percentage absolute risk reduction or risk increase conferred by 13 interventions across 10 long term conditions on 17 important outcomes. Responses were collated and presented graphically for each clinical question and analyses performed to estimate the proportion of correct responses.

Results 443 respondents, broadly representative of the British GP population, were included in the analysis. The majority of respondents demonstrated poor knowledge of the absolute benefits and harms of treatments with inaccuracies common and wide ranging. Per question, only 3.2 - 28.4% of responses were correct allowing for +/- 1% margin in ARR estimates and 10.4 – 55.6% allowing a +/- 3% margin. 65% of GPs self-reported low to very low confidence in their knowledge.

Conclusions GPs’ knowledge of the absolute benefits and harms of treatments is poor, with inaccuracies of a magnitude likely to significantly affect clinical decision making and impede meaningful conversations with patients regarding treatment choices.

This represents a barrier to the practice of EBM as it is intended. The causes are complex and lie within the system of evidence dissemination, implementation and performance management of practitioners. These will be discussed along with potential solutions.