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Re: [Synoptic-L] When is a correlation meaningful?

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  • dgentil@sears.com
    Emmanuel Fritsch @abraxa.ign.fr on 01/30/2002 04:05:46 AM Sent by: fritsch@abraxa.ign.fr To: dgentil@sears.com cc:
    Message 1 of 3 , Jan 30, 2002
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      Emmanuel Fritsch <emmanuel.fritsch@...>@... on 01/30/2002
      04:05:46 AM

      Sent by: fritsch@...


      To: dgentil@...
      cc: Synoptic-L@...

      Subject: Re: [Synoptic-L] When is a correlation meaningful?



      > If I were trying to construct some sort of forecast of one variable,
      > based on the other, .7 might be a reasonable cut off. Half of the
      > variation in one variable is explained by the other, at this level.
      > ( .5^2 = appox. .7 )

      .5^2=.25 (exactly) and .7^2=.5 (approx.)


      *****Whoops. Thanks. I'll blame dyslexia for that. :o)


      > However, our question is related to demonstrating a relationship,
      > positive or negative, exists. So for our purposes, any correlation
      > with a sufficiently large p value should be accepted.
      > [...]
      > Of course the correlations, even once accepted, could have more than
      > one possible explanation. My opinion is that the major effects are
      > related directly to authorship, but that there are other effects as
      > well, artificially raising the confidence level might be one way to
      > eliminate these, but it also makes the cut-off somewhat subjective,
      > since we are now judging what results need to be excluded.

      Some minor effects may be explaned from a composite authorship :
      if two categories are correlated with r=0.15 (and p < .000056), it
      may result from both categories sharing a common author, but only
      on a small proportion of their extent.

      a+
      manu

      ******Agreed.

      Dave Gentile
      Riverside, Illinois
      M.S. Physics
      Ph.D. Management Science candidate



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