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How does level of measurement help us in selecting correct type of correlation?

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    $\begingroup$ Welcome to CV! What do you mean by level of measurement? Your question is not clear, you can edit it with the button below to add some detail. $\endgroup$ Commented Apr 19, 2019 at 5:49
  • $\begingroup$ I think the question is related to stats.stackexchange.com/questions/119835/… $\endgroup$
    – Silverfish
    Commented Apr 19, 2019 at 10:05

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I am assuming that, by "level of measurement" you mean the "nominal, ordinal, interval, ratio" system introduced by Stevens and abused ever since.

First, I think you should be aware that these levels aren't exhaustive - that is, there are measurements that don't fit, see my blog post on this.

Notwithstanding the above, we can say some things:

  1. Nominal with anything - Unless the nominal variable takes only 2 levels, correlation doesn't really make sense. There are measures of association, but not correlation.

  2. Ordinal with ordinal, interval or ratio - It will often be best to use Spearman's rank correlation.

  3. Interval or ratio with interval or ratio - Here, Pearson's correlation is a good place to start, but you need to be aware of other possible problems (look up Anscombe's quartet for some problems that can occur).

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    $\begingroup$ (+1) Kendall's various measures of rank correlation deserve mention too. $\endgroup$
    – Nick Cox
    Commented Apr 19, 2019 at 11:49

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