Module 4 · Evidence-Based Diagnosis
4.7 Differential Diagnosis
9 min read
Having good evidence does not produce a good diagnosis by itself. What turns evidence into a conclusion that will hold is a method: enumerate the mechanisms that could produce these findings, decide what evidence would separate them, gather that evidence, and eliminate. The alternative — recognising a pattern and then collecting support for it — feels faster, produces the same answer most of the time, and fails in exactly the cases that end up contested.
Learning objectives
By the end of this lesson you will be able to:
- Enumerate the candidate mechanisms for a presentation before gathering confirmatory evidence.
- Identify the discriminating evidence for each pair of candidates.
- Work by elimination rather than confirmation.
- Record the differential so the reasoning is visible in the file.
Key terms
- Differential
- The list of mechanisms that could produce the observed findings, held open until evidence excludes members of it.
- Discriminating evidence
- Evidence whose result differs between two candidates. The only kind worth gathering once you have a differential.
- Elimination
- Excluding a candidate because evidence is inconsistent with it, rather than selecting one because evidence fits.
- Multiple causation
- Two or more mechanisms operating together. Common, routinely missed, because finding one sufficient cause usually stops the search.
Read the rest of Evidence-Based Diagnosis
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