Emergency Medicine, a risky business Part 3. How often is it acceptable for me to be wrong?

Emergency medicine is a risky business. In this continuing series looking at how we as emergency physicians look at risk we are going to spend a bit of time looking at how we feel about risk and what we consider to be acceptable in practice. If nothing else it’s a good excuse to look at a really risky video – watch this and think about whether this is acceptable.


I’m guessing that you think not (unless you are crazy IMHO), but the Isle Of Man is where I did some of my med student training and was one of the placements that convinced me that EM was for me (as I was there for the TT races in 1991). As for the question then that’s somewhat the point as risk for individuals is a personal choice, TT riders accept a level of risk which is pretty much at the highest level I can think of. Personally I would not be caught dead on the back of a motorbike, but put me on a road bike descending in little more than lycra at 50mph and I am seriously happy. Doesn’t really make sense does it.

Anyway, enough of bikes (Ed – well maybe more later). What about risk in the ED. Well, if you read the last post I think I proved that our typical process of diagnosis leads to a probability of disease rather than an absolute certainty of disease (or lack of disease). You may remember this diagram that explains how the poor clinician is looking at a combination of either true positives + false positives OR true negatives + false negatives.


So, having accepted that we are probablasticians we must then face the fact that we are wrong some of the time. If you are keeping up to speed then you will already be getting to the next question which is….

How often is it acceptable for me to be wrong?

OK, if you think never then you’re just not getting this, go back to the beginning and start again! We have to be wrong some of the time when we are investigating for things like PE or ACS. The reason is that we cannot pursue these diagnoses to the absolute max as we eventually end up causing more harm than good by exposing patients to diagnostic strategies (radiation usually), which are harmful in themselves.

risk from woodleywonderworks creative commons licence

So, are you happy with a sensitivity of 98%?

I pretty much reckon that you said yes. Not all of you would have said yes, but I reckon that you would be reasonably happy with 98% as that’s a level that is commonly considered to be a SnOUT, so sensitive that if it not positive it rules out the diagnosis. Great, but let me ask you the question a different way.

How many patients are you prepared to send home with a missed PE?

  • 1:5
  • 1:10
  • 1:25
  • 1:50
  • 1:100
  • 1:500
  • 1:1000

Not so easy now I suspect. The answer you are looking for is of course 1:50 as that is the same as a 98% sensitivity, but if you are normal the expression of this risk as a natural frequency will not fit as comfortably as the rather more palatable figure of 98% sensitivity. Don’t worry if you are uncomfortable with this. It’s normal for clinicians to be more wary about accepting risk as a natural frequency and when I’ve done this test at conferences I get completely different answers depending on whether I ask people for an opinion on a test with 98% sensitivity (they love it) or a test with an ability to spot 49/50 PE’s (not as keen) or a test which misses 1 in 50 PEs (really not very keen at all).

Now there is a whole world of literature out there on the subject of risk and risk perception. I personally like to explain risk in terms of examplar natural frequencies (I think this came from Ken Calman).

The risk is…

1 person in your house
1 person in a school class
1 person on your road
1 person in a village
1 person in your town
1 person in your city etc.

Now PE is a particularly good example for us to think of as the 98% sensitivity point is considered to be the point of clinical equipoise where pursuing the diagnosis further is just not worth it. I think that’s probably true for PE, but what other factors affect the clinical equipoise point for other diagnoses? I would consider the following.

Consequence of a missed diagnosis
The success of therapy for a confirmed diagnosis
The risks of further testing
The temporal proximity of further risk
The likelihood of getting sued (sad but true folks)
Who’s risk is it anyway?

Eh? Surely it’s just about whether you miss it or not, isn’t it?

Not really.

Consequence: There is clearly a difference in missing something like a subarachnoid bleed versus missing a fracture of the lateral malleolus. One causes pain and delayed therapy, the other may result in death. Clearly it may be more acceptable to have a lower sensitivity for less severe conditions.

Success of therapy: If we are to fret and worry about making a diagnosis then it must be to some purpose. If there is no effective therapy for the condition we are seeking to diagnose then the process of diagnosis is somewhat useless. For example I might choose to define the exact virus causing that nasty sore throat – but since my treatment is going to be exactly the same what’s the point? Similarly in conditions that are going to be fatal regardless of a diagnosis should we pursue it?

Risk of further treatment: EM physicians do not use gold standard test either because there are risks associated (angiography for PE for example) or because we cannot achieve it in the time period available to us. Once you reach the point that further exposure to testing results in more risk to the patient than just letting the patient go you should stop (a major problem in litiginous systems where errors of omission are considered to be worse than those of commission).

Temporal proximity: I’m sure that you are really interested in reducing the harms from unnecessary investigations, or at least, if you are like me, you are at this particular moment whilst we are sat here thinking about populations and risks, but in reality the risks of investigation are not linked in time to what we are doing when we have a patient in front of us. Miss a PE and we might know about it really soon! Overinvestigate with excess radiation and your patients might get more cancer in 10-50 years time. There is no doubt that the former risk weighs much more heavily on the mind and on the medico-legal insurance.

Medico-legal factors: Many of us must face the fact that our practice is influenced by the consequences to us as emergency physicians. We are actually part of the decision making as when we accept a diagnostic process that we know leads to the missing of diagnoses exposes us to a risk of medico-legal action. This is particularly important to realise in view of the temporal proximity of risk. You will get sued for missing a diagnosis this week, you won’t for giving someone cancer in 20 years time. This is a real problem as it skews your practice towards something that might be wrong for the population you are investigating.

Who’s risk are we talking about?: Thus far we have really been talking about risk from a physicians perspective, but if we leave the medico-legal stuff to one side for a second it is clear that it is the patient that experiences the risk. It is really about them at the end of the day and although we think about miss rates in terms of percentages patients either experience the process of diagnosis working correctly or not. So, whilst we think about a % chance of getting it right the patient only experiences a dichotomous outcome.

So what?

So, in summary risk perception and acceptance is really quite complex depending on what you are looking at and who you are, and even how it is expressed. Bear this in mind as we move to part 4 to discuss the consequences of missing a diagnosis.



For all posts in this series click here

Risky Business Part 1 You are not a diagnostician.

Risky Business Part 2 What does a test result really mean?

Risky Business Part 3 Is it acceptable to miss some diagnoses?

Risky Business Part 4 How many patients do we miss (and does it matter)?

Risky Business Part 5 Does a correct diagnosis mean that the therapy will work?

Risky Business Part 6 How many steps to disaster?

Risky Business Part 7. Risk Proximity


Before you go please don’t forget to…



Cite this article as: Simon Carley, "Emergency Medicine, a risky business Part 3. How often is it acceptable for me to be wrong?," in St.Emlyn's, October 19, 2012, https://www.stemlynsblog.org/em-a-risky-business-part-3/.

3 thoughts on “Emergency Medicine, a risky business Part 3. How often is it acceptable for me to be wrong?”

  1. Pingback: Emergency Medicine - a risky business part 1 - St Emlyns

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  3. Pingback: When is a Door Not a Door? Bias, Heuristics & Metacognition

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