prase comments on Causality does not imply correlation - Less Wrong

13 Post author: RichardKennaway 08 July 2009 12:52AM

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Comment author: prase 08 July 2009 01:43:31PM *  0 points [-]

The standard form for correlation coefficient is

cov(x,y)=N(<xy>-<x><y>)

where N is normalisation; it seems that you suppose that <f>=0 and <f'> finite, then. <f>=0 follows from boundedness, but for the derivative it's not clear. If <f'> on (a,b) grows more rapidly than (b-a), anything can happen.

Comment author: RichardKennaway 08 July 2009 01:58:33PM 0 points [-]

If <f'> on (a,b) grows more rapidly than (b-a)

This cannot happen. f is assumed bounded. Therefore the average of f' over the interval [a,b] tends to zero as the bounds go to infinity.

The precise, complete mathematical statement and proof of the theorem does involve some subtlety of argument (consider what happens if f = sin(exp(x))) but the theorem is correct.