Letters

Communicating risks through analogies

BMJ 2003; 327 doi: http://dx.doi.org/10.1136/bmj.327.7417.749 (Published 25 September 2003) Cite this as: BMJ 2003;327:749
  1. Adrian Edwards, reader (a.g.k.edwards{at}swan.ac.uk)
  1. Primary Care Group Swansea Clinical School, University of Wales, Swansea SA2 8PP

    EDITOR–Articles in this theme issue have described approaches that try to enhance the communication of risk by developing communication skills, using decision aids, and simplifying the representation of information. But when clinicians talk about actual risks with individual patients they often use analogies. We asked visitors to bmj.com to tell us some of their analogies.1 Many of their responses addressed screening and chronic disease–perhaps because they are both particularly fraught with difficulty.



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    The value of illustrations was reinforced by Barth, a surgeon: he described how he gives patients a digital picture of their scan that includes a risk calculation. This, of course, also indicates the extent of disease.

    Many of the examples from readers try to convey the size of a risk. People know, for example, that smoking is a risk but find it difficult to comprehend its magnitude. Mackay relates how Richard Peto (responsible for many of the big studies on the effects of smoking) tosses a coin and slaps it on the back of his hand to illustrate to his audience the (true) 50% risk of being killed from long term tobacco smoking. “It always produces a gasp of surprise.”

    Clinicians may be faced with conveying very small risks. Markowicz relates how he sometimes engages in the following dialogue:

    “Do you know what is the biggest risk you face in connection with this procedure?

    “No, doctor. What is it?

    “Driving to the test!”

    Similarly, Anton compares mobile phones with genetically modified (GM) food. Both have a (probably) small, unquantifiable, and theoretical risk of causing serious health problems. “No one wants to eat GM food, everyone wants a mobile phone.” (Bellaby explores some of these discrepancies further (p 725).)2

    In all screening programmes the accuracy of the screening test is limited by its specificity and sensitivity. Nottingham relates two analogies to try to explain this phenomenon. The first analogy shows how most abnormalities are picked up but a few slip through the net, sometimes with disastrous results:

    “Imagine you are a fire fighter called to a burning house. From inside you hear screaming. You manage to rescue x of the yoccupants but despite your best efforts z perish. Should you be hailed as a hero or indicted for homicide?”

    The second analogy emphasises that by increasing the sensitivity more people without disease will be investigated while by increasing the specificity more people with disease will be missed:

    “Convict everyone who is tried by a jury and fewer criminals will walk the streets but some innocent people will get locked up. Move too far the other way and there will be fewer wrongful convictions but some guilty people will get away with it. This doesn't make the lawyers, the judges, or the juries incompetent or negligent: it's an inevitable part of the system. Change the system and things could be better or worse.”

    Dawson considers abnormal cervical smear test results, particularly women's concerns about why their smear test needs to be repeated sooner than expected. To answer the question, “If I've got cancer why isn't it being treated?” he draws on the analogy of blood pressure measurement.

    “If the blood pressure is ‘plumb normal’ then there's no need to repeat for three years; if it's obviously abnormal then we need to make sure but would expect to treat it. Often the blood pressure is not low enough to consider normal or high enough to investigate and treat. In those cases we arrange another check a little later. Depending on the value then, we either treat or continue closer follow up until we are happy that all is normal.”

    Other respondents considered chronic diseases. Mukhopadhyay conveys the multiplication of risks in diabetes when several risk factors are present by considering the risks of breaking a limb on leaving a house:

    “A healthy person gets out of the house through the door. If you're diabetic, you are jumping from the first floor. If you also have high blood pressure, you're jumping from the second floor… and so on. Finally, if you smoke in addition, you're jumping from the top of a five storey building.

    “And, to make people understand the impact of control, I mention that they can come down the stairs by controlling their risk.”

    Many of Bieber's patients are from professional groups, and he likens the process of improving lifestyle and risk factors to making decisions about a retirement portfolio.

    “With an investment counsellor, a person periodically assesses how their assets are invested and what the anticipated yield will be over time. If a shift in assets from 4% yield to 6% yield is easy and available, over 20 years of investing, great profits can be expected. Likewise, healthy decisions (cholesterol control, weight modification, blood pressure control, etc) can improve a patient's chances of having a full ‘portfolio’ and healthy body when retirement time comes in 20 years. Each small incremental improvement, over 20 years, can offer compounding results statistically.”

    Finally, two correspondents raise interesting issues about the framing of risk and the limits to certainty.

    Arnold writes of a mother who had a baby with spina bifida. “She asked me the risk of a recurrence with a second pregnancy. As I had no idea, I consulted a relevant book. The risk stated was 1 in 10. I told her that she had a 90% chance of having a normal baby. She happily ran out of the surgery, soon became pregnant, and produced an infant with a normal spine.

    “I relate this anecdote because I was berated when I recounted this story in a discussion of risk, at a meeting with ‘medical consumers.’ I was told that I had lied to my patient. Had I?”

    Garcia communicates cardiovascular risk to his patients using the analogy of car crashes. He explains what could happen if they do not wear a seat belt, observe the speed limit, or follow traffic lights, etc. It does not mean that they will die in a car crash. Similarly, wearing a seat belt, observing the speed limit, or complying with traffic lights does not mean that they won't. However, among hundreds of people in the first population and hundreds in the second, the number of traffic deaths will definitely be higher in the first group.

    Moreover, he adds, “You should know that whatever the behaviour you adopt you will never know what would have happened should you have adopted the other way.”

    Footnotes

    • Competing interests None declared.

    References