Show HN: If Correlation doesn't imply causation, then, what does?

michaelnielsen.org

15 pointspoxwole3 comments

"For the notion of causality to make sense we need to constrain the class of graphs that can be used in a causal model. Obviously, it’d make no sense to have loops in the graph:

We can’t have X causing Y causing Z causing X! At least, not without a time machine. Because of this we constrain the graph to be a directed acyclic graph, meaning a (directed) graph which has no loops in it."

Of course you can have loops, no need for time machine:

https://en.wikipedia.org/wiki/Virtuous_circle_and_vicious_ci...

https://en.wikipedia.org/wiki/Causal_loop_diagram

https://en.wikipedia.org/wiki/Positive_feedback

The examples you have posted do not contradict what the author is saying. A feedback cycle is something like: a quantity A at time t1 given by A(t1) influences another quantity B(t2) which in turn influences A(t3). Here t3 > t2 > t1.

We would run into causality issues if t3 = t1, but that doesn’t happen.

In your examples X and Z are events of the same kind but not the same event.

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