Communicating risk
A hazard is something that has the potential to cause harm. A risk is the likelihood a hazard will cause harm.
Doctors deal with risk constantly. A solid understanding of risk and an ability to communicate risk to patients and the public is vital.
When considering risk, the likelihood of the outcome is not the only important consideration - we also need to consider the consequences. Climbers who free solo (climb without ropes) are familiar with this distinction when assessing the risk of falling. If the climber is on a route they consider to be easy and therefore have a low risk of falling they may tolerate significant consequences of a fall (such as death). On the other hand, lottery players accept that their risk of not winning the lottery is very high - but the consequences of failing to win the lottery are very low (you are £5 poorer).
Risk metrics
A number of different metrics can be used to communicate risk.
| Metric | Calculation |
|---|---|
| Probability | $$P(event)=\frac{Positive outcomes}{All possible outcomems}$$ |
| Absolute risk reduction | |
| Relative risk reduction | |
| Odds | |
| Odds ratio | |
| Likelihood ratio | |
| Number needed to treat |
Numerical literacy among doctors and patients
The probability yardstick
A huge number of English phrases can be used to convey how likely something is. Examples include 'remote chance', 'highly unlikely', 'may happen', 'better than even', 'realistic possibility', 'probable' and 'almost certain.' There are many more!
Some of these phrases mean very different things to different people. The importance of this in medicine is not hard to appreciate. When I tell a patient they have little chance that their headache is due to an aneurysm - are the risks assumed by the patient numerically similar to those in my mind?
You can get a sense of where your estimates of risk from certain phrases might fall by completing a quiz at https://probability.kucharski.io/. An example of the output is this is shown below.
Ensuring we are all on the same page with respect to risk is not just a problem in Medicine. The UK Intellegence Services have produced a probability yardstick that is used to standardise assessment.
In addition to the probability itself, a measure of confidence in the assessment is also assigned (low, medium or high).
Cognitive biases in risk assessment
Framing is an important component of risk assessment.
Practical advice for communicating risk
1) Risk should be conveyed with information on consequence and confidence to aid decision making. 2) Risks should be framed appropriately (bilaterally if possible). 3) Risk should be communicated to patients using natural frequencies.