Degrees of freedom

(Sep 16, 2008)

In an earlier post questioning whether we still need standard tables, we used the AIC to choose between models.  For the AIC we assign a "cost" to the inclusion of extra parameters, and I had counted each mortality rate actually used in the model-fitting as a parameter.  However, there is no set approach for this, and there are a number of arguable positions which could be taken:

  1. Count each mortality rate in the table as a parameter.  This would arise because the selection of the table is supposed to be done before fitting any model.  However, it seems harsh to count rates which are not actually used.
  2. Count each mortality rate actually used as a parameter.  This is my preferred approach, but the rates themselves…

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Tags: degrees of freedom, AIC, standard table

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