Coincidence, Correlation & Causation

Sometimes things happen or occur that seem to be related in some way. There is a hierarchy of possibilities of what may be the reason.

  • Coincidence
  • Correlation
  • Causation

The first, and often most likely, is that it is a coincidence and nothing more. Having tossed a coin and got a head does not alter the probability of the next toss being a head too or the one after that…

If that happens we would likely ascribe this to luck and not some issue with the coin or the tossing. Most often when things occur that seem to be related the most likely explanation is coincidence. Of course if the heads kept coming up then we would become suspicious and look for some independent evidence, not just the sequence of heads, about the coin or the toss.

In a previous post I wrote about the difference between correlation and causation and how to distinguish them. This can be quite tricky, and the causal relationship is more difficult to prove than a correlation. Similarly if there are just a few occurrences it is difficult to discern coincidence from correlation or causation. Even if there are more occurrences it can still be tricky to prove it is anything but coincidence.

So how to proceed? Be open to the alternative explanations of when things seem to be related.

  • If there is no other independent evidence for a relationship between them, then the best judgement is a coincidence.
  • If we have some other independent evidence that they are related, then we can move up the hierarchy and consider they might be correlated in the way suggested by the independent evidence we have.
  • Only if we have some strong evidence that there is a causal relationship are we justified in going to the top of the hierarchy and attributing a causal relationship: that something is causing this to happen.

We should never consider a correlation explanation and much less a causal relationship unless we have some independent evidence. This is how conspiracy theories and fake news reports emerge.

We all like to think that there is a meaning to everything in life and sometimes there is, but it is often the case that there is no meaning and it is just coincidence.


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