Graphics Reference
In-Depth Information
We present many examples of structured sets of graphs that convey and support
statistical analyses. Structured sets of graphs can be drawn with any modern sta-
tistical sotware system with graphics capabilities. We use S-Plus and R, two di-
alects of the S language that offer substantial capabilities for producing graphs cus-
tomized to the particular needs and visions of the analyst. We emphasize two ba-
sic paradigms for constructing structured graphs: Cartesian products and the Trellis
paradigm. Our sotware for all examples in this article is available from Heiberger
and Holland (
).
Introduction
6.1
S-Plus and R offer users substantial capabilities to customize graphs to their par-
ticular needs and visions when they are accessed using command language rather
than their graphical user interfaces (GUIs). Production sotware, that is, sotware
already developed by someone else, needs to be standardized, packaged, and restric-
tive, allowing the user less control. Analysts occasionally require a graph unlike any
readily available elsewhere. We recommend that serious data analysts invest time in
becoming proficient in writing code rather than using GUIs. Users of a GUI are lim-
ited to the current capabilities of the GUI. While the design of GUIs will continually
improve, their capabilities will always remain far behind what skilled programmers
can produce. Even less-skilled analysts can take advantage of cutting-edge graphics
by accessing libraries of graphing functions such as those accompanying our text or
available at Statlib and elsewhere on the Internet.
Ourgraphicaldisplaysaredesignedforelementarytointermediatestatisticalanal-
yses,but the graphs themselves are relatively sophisticated constructions. Our exam-
ples extend the concept of a structured presentation of plots of different sets of vari-
ables, or of different parametric transformations of the same set of variables. Several
oftheexamples extendtheinterpretation of themodelformula, that is,thesemantics
of the formula, to allow easier exposition of standard statistical techniques.
Our examples are taken from several sources. hese include classical and recent
examples from the statistical literature, standard texts in statistics, the authors' text-
book Heiberger and Holland (
) (referred to in the sequel as HH), and projects
on which the authors have worked as consulting statisticians.
Cartesian Products
and the Trellis Paradigm
6.2
A feature common to many of the displays is the Cartesian product principle behind
their construction.
