[S] drop1() and TYPE III SS

Bill Shipley (bshipley@courrier.usherb.ca)
Thu, 26 Feb 1998 10:08:06 -0500


SAS-like "type III" sums of squares can be obtained with the
drop1(fit.aov,~.) function, where fit.aov is an object producted from the
aov() function.
However, I sometimes find that some terms are left blank when using doing
this. for instance, here are the results of the last line from the
drop1(fit.aov,~.) output of a recent analysis:

Pr(F)
<none>
Espece 0.000000000
lumiere
azote
Espece:lumiere 0.000070067
Espece:azote 0.001591243
lumiere:azote
Espece:lumiere:azote 0.000000364

where Espece, lumiere and azote were factors in an unbalanced design. Note
that probability levels were calculated only for terms involving Espece.
Why is that and how can it be corrected so that drop1() will output the
results for the other terms?
Bill Shipley
Departement de Biologie
Universite de Sherbrooke
Sherbrooke (Quebec)
CANADA J1K 2R1
bshipley@courrier.USherb.ca
voix: 819-821-8000 poste 2079
telecopieur: 819-821-8049
Visitez notre site WEB : http://www.usherb.ca/SCES/BIO/index.html

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