| % File src/library/graphics/man/assocplot.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2018 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{assocplot} |
| \alias{assocplot} |
| \encoding{UTF-8} |
| \title{Association Plots} |
| \description{ |
| Produce a Cohen-Friendly association plot indicating deviations from |
| independence of rows and columns in a 2-dimensional contingency |
| table. |
| } |
| \usage{ |
| assocplot(x, col = c("black", "red"), space = 0.3, |
| main = NULL, xlab = NULL, ylab = NULL) |
| } |
| \arguments{ |
| \item{x}{a two-dimensional contingency table in matrix form.} |
| \item{col}{a character vector of length two giving the colors used for |
| drawing positive and negative Pearson residuals, respectively.} |
| \item{space}{the amount of space (as a fraction of the average |
| rectangle width and height) left between each rectangle.} |
| \item{main}{overall title for the plot.} |
| \item{xlab}{a label for the x axis. Defaults to the name (if any) of |
| the row dimension in \code{x}.} |
| \item{ylab}{a label for the y axis. Defaults to the name (if any) of |
| the column dimension in \code{x}.} |
| } |
| \details{ |
| For a two-way contingency table, the signed contribution to Pearson's |
| \eqn{\chi^2}{chi^2} for cell \eqn{i, j} is \eqn{d_{ij} = (f_{ij} - |
| e_{ij}) / \sqrt{e_{ij}}}{d_{ij} = (f_{ij} - e_{ij}) / sqrt(e_{ij})}, |
| where \eqn{f_{ij}} and \eqn{e_{ij}} are the observed and expected |
| counts corresponding to the cell. In the Cohen-Friendly association |
| plot, each cell is represented by a rectangle that has (signed) height |
| proportional to \eqn{d_{ij}} and width proportional to |
| \eqn{\sqrt{e_{ij}}}{sqrt(e_{ij})}, so that the area of the box is |
| proportional to the difference in observed and expected frequencies. |
| The rectangles in each row are positioned relative to a baseline |
| indicating independence (\eqn{d_{ij} = 0}). If the observed frequency |
| of a cell is greater than the expected one, the box rises above the |
| baseline and is shaded in the color specified by the first element of |
| \code{col}, which defaults to black; otherwise, the box falls below |
| the baseline and is shaded in the color specified by the second |
| element of \code{col}, which defaults to red. |
| |
| A more flexible and extensible implementation of association plots |
| written in the grid graphics system is provided in the function |
| \code{\link[vcd]{assoc}} in the contributed package \CRANpkg{vcd} |
| (Meyer, Zeileis and Hornik, 2006). |
| } |
| \seealso{ |
| \code{\link{mosaicplot}}, \code{\link{chisq.test}}. |
| } |
| \references{ |
| Cohen, A. (1980), |
| On the graphical display of the significant components in a two-way |
| contingency table. |
| \emph{Communications in Statistics---Theory and Methods}, \bold{9}, |
| 1025--1041. |
| \doi{10.1080/03610928008827940}. |
| |
| Friendly, M. (1992), |
| Graphical methods for categorical data. |
| \emph{SAS User Group International Conference Proceedings}, \bold{17}, |
| 190--200. |
| \url{http://www.math.yorku.ca/SCS/sugi/sugi17-paper.html} |
| |
| Meyer, D., Zeileis, A., and Hornik, K. (2006) |
| The strucplot Framework: Visualizing Multi-Way Contingency Tables with |
| \pkg{vcd}. |
| \emph{Journal of Statistical Software}, \bold{17(3)}, 1--48. |
| \doi{10.18637/jss.v017.i03}. |
| } |
| \examples{ |
| ## Aggregate over sex: |
| x <- margin.table(HairEyeColor, c(1, 2)) |
| x |
| assocplot(x, main = "Relation between hair and eye color") |
| } |
| \keyword{hplot} |