Re: GLM vs unbalanced designs

[Jason Stover]

On Tue, Sep 27, 2011 at 02:02:02PM +0000, John Darrington wrote:
> Does anyone have any ideas about what we need to do different in the face of
> non-equal sample sizes?  I've tried the obvious things, like using harmonic
> means instead of arithmetic ones. But so far no luck.  And quite why the 
> intercept
> should be different, I don't understand.

I'll take a look at it.

> 
> J'
> 
> 
> 
> data list notable
>    fixed 
>   /dmethod 1 illum 3 score 5-6.
> begin data.
> 1 1  3
> 1 1  4
> 1 1  6
> 1 1  7
> 1 2  5
> 1 2  6
> 1 2  6
> 1 2  7
> 1 2  7
> 1 3  4
> 1 3  6
> 1 3  8
> 1 3  8
> 1 4  8
> 1 4 10
> 1 4 10
> 1 4  7
> 1 4 11
> 2 1  2
> 2 1  3
> 2 1  4
> 2 2  3
> 2 2  5
> 2 2  6
> 2 2  3
> 2 3  9
> 2 3 12
> 2 3 12
> 2 3  8
> 2 4  9
> 2 4  7
> 2 4 12
> 2 4 11
> end data.
> 
> variable labels score 'Accuracy Score'.
> 
> glm score by illum dmethod
>   /method=sstype(3)
>   /intercept=include
>   /criteria=alpha(.05)
>   /design.
> 
> 
> Actual Results:
> 
> 
> Tests of Between-Subjects Effects
> #===============#=======================#==#===========#=======#====#
> #     Source    #Type III Sum of Squares|df|Mean Square|   F   |Sig.#
> #===============#=======================#==#===========#=======#====#
> #Corrected Model#                184.250| 7|     26.321|  8.061|.000#
> #Intercept      #               1589.121| 1|   1589.121|486.690|.000#
> #illum          #                150.592| 3|     50.197| 15.374|.000#
> #dmethod        #                   .113| 1|       .113|   .035|.854#
> #illum * dmethod#                 33.212| 3|     11.071|  3.391|.034#
> #Error          #                 81.629|25|      3.265|       |    #
> #Total          #               1855.000|33|           |       |    #
> #Corrected Total#                265.879|32|           |       |    #
> #===============#=======================#==#===========#=======#====#
> 
> 
> 
> 
> Expected Results:
> 
> Tests of Between-Subjects Effects
> 
> Dependent Variable:     Type III      df      Mean Square     F           Sig.
> Accuracy Score Source         Sum of Squares
> 
> Corrected Model       195.029(b)      7       27.861          9.831      .000 
> Intercept             1478.432        1       1478.432        521.677    .000 
> ILLUM                         158.951         3       52.984          18.696  
>    .0001
> DMETHOD               6.176E-02       1       6.176E-02       .022       .8842
> ILLUM * DMETHOD       43.991          3       14.664          5.174      .0063
> Error                         70.850          25      2.834   
>       
> Total                         1855.000        33      
>       
> Corrected Total       265.879         32      
> -- 
> PGP Public key ID: 1024D/2DE827B3 
> fingerprint = 8797 A26D 0854 2EAB 0285  A290 8A67 719C 2DE8 27B3
> See http://pgp.mit.edu or any PGP keyserver for public key.
> 



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