Communicating Risk (BMJ 2012)

“Communicating Risk” is the title of a clinical review in the BMJ on June 23rd 2012. The article summarises some of the different ways in which evidence can be presented, and discusses the relative merits of using Relative Risk Reduction (RRR), Absolute Risk Reduction (ARR) and Number Needed to Treat (NNT). Within Cochrane Systematic reviews the new Summary of Findings tables are designed to take relative measures (such as Odds Ratios and Relative Risks) from systematic reviews and turn them into Absolute Risk Reductions, as the benefits and risks of a treatment can then be directly compared with each other. Visual Rx will achieve the same thing and generate a Cates plot to use pictorial evidence alongside the numbers (such as Figure 2 in the BMJ article). The Cates plots from the NPC decision aid on statins is shown for a patient with a 20% risk of a cardiovascular event over 10 years, but most Primary care computer systems will now generate a personalised risk for the patient. This is why the simple data entry screen (labelled statin calculator) has been put in the left margin of our website, so clinicians or patients can enter their own 10 year CVD risk and see how much difference taking a statin would make to them.

The BMJ article also discusses the use of natural frequencies and the evidence from Akl and colleagues that clinicians and patients find natural frequencies easier to understand than probabilities. Finally they also point out that those patients who use decision aids, such as those provided by the NHS National Prescribing Centre are “consistently more ready to make a decision than those receiving usual care”.

The rapid responses also make interesting reading. Akl wonders if it is time for RRR to be abandoned, and Miriam Pryke questions whether it is ever right to “endeavour to change beliefs or promote behavioural change”, rather than just present the evidence.

An article in the BMJ in February 2012 on “Shared decision making” also makes interesting reading and covers many of the same issues from a slightly different perspective, as well as featuring a Cates plot used by the Mayo clinic to explain the benefits of statins.