Quick Tip: Watch out for the severity bias when analyzing medical device risk
Risk is a combination of severity and probability. It is not either-or, it is both.
Risk (of harm) associated with the use of a medical device is characterized as a combination of the probability of occurrence and the severity of that harm.
But how do you combine the two? There is no mathematical equation to quantify a risk level in terms of its probability of occurrence and the severity of outcome. Current industry practice is to assign 3-5 qualitative levels for the probability of harm (POH) and the severity of harm (S). In a 5x5 risk matrix, this method results in a total of 25 unique combinations of S and POH, each corresponding to an individual risk level (R1, R2….R25 etc.).
A natural question to ask is whether R1(S=5, POH=1) should be treated the same way as R2 (S=1, POH =5) for the purpose of making judgments about risk mitigation and risk acceptability.
When asked, most risk practitioners in the industry tend to consider R1 to be much more significant than R2, because it corresponds to the highest severity level on a 5 point scale. This approach reflects a dominant mindset that severity of harm (S) has a higher weight in the risk equation.
There are two problems with a severity-only mindset:
First, we need to be highly accurate in assigning severity levels to potential harms and use them consistently in our risk analysis. This is easier said than done!
Second, a severity-only focus undermines the potential for risk reduction through robust design and reliability improvements. Reliability is the twin sibling of safety!
When we focus more on severity, to the extent that we undermine or ignore the probability of occurrence, we are managing risks with one hand tied behind our back!
At times, it may be appropriate to focus on high severity outcomes regardless of their probability of occurrence. But in many other situations, a more balanced approach is preferred.
