Re: GLM factorial analysis

[John Darrington]

On Fri, Aug 12, 2011 at 05:37:20PM -0400, Jason Stover wrote:
     
     I looked into this problem.  Briefly stated, this happens because the
     meaning of "type 3 sums of squares" changes in the presence of
     interactions.  The fix should be simple enough, but requires get_ssq
     to know which variables, if any, went into an interaction. Is there an
     easy way to do this?

Yes.

struct interaction which is defined in src/math/interaction.h is a transparent
struct defined as follows:

struct interaction
{
  size_t n_vars;
  const struct variable **vars;
};


So it's easy to add a function which checks if a variable is a member of an 
interaction. 

Perhaps in the future, we should change the implementation of interactions to 
use a hash
table, so that looking up a variable can be done in constant time.  However for 
now, a 
linear search should do.

J'
     
     -Jason
     
     > 
     > J'
     > 
     > On Mon, Jul 25, 2011 at 02:29:07PM -0400, Jason Stover wrote:
     >      On Mon, Jul 25, 2011 at 09:11:21AM +0000, John Darrington wrote:
     >      > The sum of squares for factors with interactions are correct, and 
all the degrees of
     >      > freedome are correct.  Unfortunately the ssq for factors without 
interactions are 
     >      > wrong (my experiments showed 3.0 and 3.5 times too high) if the 
analysis also 
     >      > includes interactions between those factors.
     >      > 
     >      > However, if the analysis is run on the individual variables, 
without the interactions,
     >      > then the results are correct.  
     >      > 
     >      > So I think the get_ssq function needs some more work.
     >      
     >      Can you send syntax and output that shows the problems?
     > 
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