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Comment by conjectures | Hacker News Reader

This comes down to vocabulary.

If by correlation we mean Pearson correlation (linearly related) the answer is no.

If by correlation we mean some hand-waving association between A and B then yes. Since if A causes B there is some hand-waving association between them, namely causation.

I suggest we reserve 'correlation' for linear relationships and stop using it in the second sense. It's unhelpful and confusing.

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Two problems: first is that casual association may be invisible to even hand-waving criteria; think good crypto PRNG output which is fully determined by seed and is serial number, but the parameters are practically unfittable from the data because the function is so chaotic. Second thing is that the more hand-waving you allow the more totally incidental relations will look "true". With a modern amounts of hypotheses, even Pearson correlation often becomes useless in this manner.

mbq, I would not contradict your points.

Though first sense 'correlation' could well be useless in many cases at least I know what it means.

The second sense is perfidious as it's virtually impossible to deny there's a 'correlation' between any two things since the term so poorly defined.

Note that I am criticising the idea of "general" or "intuitive" correlation; actually useful correlation measures (like Pearson or Spearman) will be just always tied to some model of dependence. This way it cannot be directly tied to the obviously absolute dependence.

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