Ord_plot {vcd} | R Documentation

## 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),
      name = "Ord_plot", newpage = TRUE, pop = TRUE, ...)
    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.
`name` | name of the plotting viewport.
`newpage` | logical. Should `grid.newpage` be called before plotting?
`pop` | logical. Should the viewport created be popped?
`...` | 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 Achim.Zeileis@R-project.org

### 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)

    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)

[Package vcd version 0.9-6 Index]