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Definitions: "effectDegreesOfFreedom" & "errorDegreesOfFreedom" #277

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nicholst opened this issue Mar 24, 2015 · 2 comments
Open

Definitions: "effectDegreesOfFreedom" & "errorDegreesOfFreedom" #277

nicholst opened this issue Mar 24, 2015 · 2 comments

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@nicholst
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These two weren't ever defined. What do people think? @jbpoline, @gllmflndn?

  • nidm:effectDegreesOfFreedom: Degrees of freedom of the effect.

    In the context of a general linear model, the effect degrees of freedom is the rank of the contrast. For example, a contrast comprising of a vector has effect degrees of freedom of 1 and can be tested with a F-test with numerator degrees of freedom of 1.
  • nidm:errorDegreesOfFreedom: Degrees of freedom of the error.

    In the context of a general linear model, the error degrees of freedom are the number of observations less the rank of the design matrix.

Note the awkward description of "contrast consisting of ... vector"; we have not defined whether a contrast matrix consists of rows or columns of contrast vectors, and hence I left it vague.

@nicholst
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I have re-read my definition and remain happy with it 21 days later. +1 :)

@cmaumet
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cmaumet commented Apr 20, 2015

The suggested update was implemented in #318 where the term status was set to "pending final vetting". This issue remains open to continue the discussion until we reach a consensus.

@khelm khelm added Terms and removed Terms labels Sep 26, 2017
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