Graphical Analysis of Variance
Description
This small collection of functions provides distinctive
graphics for display of anova results. The two principal
functions are granova.1w (a graphic for one way anova) and
granova.2w (a corresponding graphic for two way anova). These
functions were written to display data for any number of
groups, regardless of their sizes (however, very large data
sets or numbers of groups are likely to be problematic). For
these two functions a specialized approach is used to construct
data-based contrast vectors with respect to which anova data
are displayed. The result is that the graphics use straight
lines, and flat surfaces, to help ensure clear interpretations
while being faithful to the standard effect tests in anova; the
graphic results are complementary to standard summary tables
for these two basic kinds of analysis of variance. Two
additional functions are granova.ds (for comparing two
dependent samples of data), and granova.contr (which provides
graphic displays for a priori contrasts). All functions provide
relevant numerical results to supplement the graphic displays
of anova data. The graphics based on these functions are aimed
at students and non-statistician analysts; but they can be
generally helpful for identifying outliers, clusters, trends or
the role of non-linear transformations of data. In the case of
granova.1w and granova.ds especially, several arguments have
been provided to facilitate construction of graphics that
accommodate diverse features of data, and their corresponding
display requirements.