Graphics Reference
In-Depth Information
Boxplots
6.7
Assessing Three-way Interaction
6.7.1
Cochran and Cox ( ) report on an experiment to assess the effect of electrical
stimulationtopreventtheatrophyofmuscletissueinrats.hisexperimentcontained
aresponsevariable wt.d (weightoftreatedmuscle),acovariate wt.n (weightofun-
treated muscle), and three factors, current , n.treat ,and minutes .hereare
two replications of the entire experiment. It is desired to model wt.d as a function
of the other variables. he datafile is (hh/datasets/muscle.dat).
Figure . is designed to assess whether there is a significant three-way interac-
tion. he three-way interaction is not significant in this example. If there were a sig-
nificant three-wayinteraction, thepatterns inboxplotsinadjacent rowsandcolumns
would not be the same. For example, we note a hint of a difference in the y.adj ~
minutes behavior across panels. It has a negative slope in the galvanic ~ 3
panel and a positive slope in the faradic ~ 3 panel, but a positive slope in the
galvanic ~ 6 panelandanegative slopeinthe faradic ~ 6 panel.However,
an ANOVA table for a full model containing the three-factor interaction indicates
Figure . . hree-way interactions of all effects. One of the ( ! = ) possible orderings (Files:
hh/dsgn/code/cc .s, hh/csc/code/cc -csc.s)
 
Search WWH ::




Custom Search