Ord_plot: Ord Plots

In vcd: Visualizing Categorical Data

Ord Plots

Description

Ord plots for diagnosing discrete distributions.

Usage

Ord_plot(obj, legend = TRUE, estimate = TRUE, tol = 0.1, type = NULL,
  xlim = NULL, ylim = NULL, xlab = "Number of occurrences",
  ylab = "Frequency ratio", main = "Ord plot", gp = gpar(cex = 0.5),
  lwd = c(2,2), lty=c(2,1), col=c("black", "red"),
  name = "Ord_plot", newpage = TRUE, pop = TRUE,
  return_grob = FALSE, ...)
Ord_estimate(x, type = NULL, tol = 0.1)

Arguments

obj	either a vector of counts, a 1-way table of frequencies of counts or a data frame or matrix with frequencies in the first column and the corresponding counts in the second column.
legend	logical. Should a legend be plotted?.
estimate	logical. Should the distribution and its parameters be estimated from the data? See details.
tol	tolerance for estimating the distribution. See details.
type	a character string indicating the distribution, must be one of "poisson", "binomial", "nbinomial" or "log-series" or NULL. In the latter case the distribution is estimated from the data. See details.
xlim	limits for the x axis.
ylim	limits for the y axis.
xlab	a label for the x axis.
ylab	a label for the y axis.
main	a title for the plot.
gp	a "gpar" object controlling the grid graphical parameters of the points.
lwd, lty	vectors of length 2, giving the line width and line type used for drawing the OLS line and the WLS lines.
col	vector of length 2 giving the colors used for drawing the OLS and WLS lines.
name	name of the plotting viewport.
newpage	logical. Should grid.newpage be called before plotting?
pop	logical. Should the viewport created be popped?
return_grob	logical. Should a snapshot of the display be returned as a grid grob?
...	further arguments passed to grid.points.
x	a vector giving intercept and slope for the (fitted) line in the Ord plot.

Details

The Ord plot plots the number of occurrences against a certain frequency ratio (see Friendly (2000) for details) and should give a straight line if the data comes from a poisson, binomial, negative binomial or log-series distribution. The intercept and slope of this straight line conveys information about the underlying distribution.

Ord_plot fits a usual OLS line (black) and a weighted OLS line (red). From the coefficients of the latter the distribution is estimated by Ord_estimate as described in Table 2.10 in Friendly (2000). To judge whether a coefficient is positive or negative a tolerance given by tol is used. If none of the distributions fits well, no parameters are estimated. Be careful with the conclusions from Ord_estimate as it implements just some simple heuristics!

Value

A vector giving the intercept and slope of the weighted OLS line.

Author(s)

Achim Zeileis [e-mail]

References

J. K. Ord (1967), Graphical methods for a class of discrete distributions, Journal of the Royal Statistical Society, A 130, 232–238.

Michael Friendly (2000), Visualizing Categorical Data. SAS Institute, Cary, NC.

Examples

## Simulated data examples:
dummy <- rnbinom(1000, size = 1.5, prob = 0.8)
Ord_plot(dummy)

## Real data examples:
data("HorseKicks")
data("Federalist")
data("Butterfly")
data("WomenQueue")

## Not run: 
grid.newpage()
pushViewport(viewport(layout = grid.layout(2, 2)))

pushViewport(viewport(layout.pos.col=1, layout.pos.row=1))
Ord_plot(HorseKicks, main = "Death by horse kicks", newpage = FALSE)
popViewport()

pushViewport(viewport(layout.pos.col=1, layout.pos.row=2))
Ord_plot(Federalist, main = "Instances of 'may' in Federalist papers", newpage = FALSE)
popViewport()

pushViewport(viewport(layout.pos.col=2, layout.pos.row=1))
Ord_plot(Butterfly, main = "Butterfly species collected in Malaya", newpage = FALSE)
popViewport()

pushViewport(viewport(layout.pos.col=2, layout.pos.row=2))
Ord_plot(WomenQueue, main = "Women in queues of length 10", newpage = FALSE)
popViewport(2)

## End(Not run)

## same
mplot(
  Ord_plot(HorseKicks, return_grob = TRUE, main = "Death by horse kicks"),
  Ord_plot(Federalist, return_grob = TRUE, main = "Instances of 'may' in Federalist papers"),
  Ord_plot(Butterfly, return_grob = TRUE, main = "Butterfly species collected in Malaya"),
  Ord_plot(WomenQueue, return_grob = TRUE, main = "Women in queues of length 10")
)

vcd documentation built on Sept. 17, 2024, 1:08 a.m.