plot.gnm | R Documentation |

Five plots are available: a plot of residuals against fitted values, a
Scale-Location plot of *sqrt{| residuals |}*
against fitted values, a Normal Q-Q plot, a plot of Cook's distances
versus row labels, and a plot of residuals against leverages. By
default, all except the fourth are produced.

## S3 method for class 'gnm' plot(x, which = c(1:3, 5), caption = c("Residuals vs Fitted", "Normal Q-Q", "Scale-Location", "Cook's distance", "Residuals vs Leverage"), panel = if (add.smooth) panel.smooth else points, sub.caption = NULL, main = "", ask = prod(par("mfcol")) < length(which) && dev.interactive(), ..., id.n = 3, labels.id = names(residuals(x)), cex.id = 0.75, qqline = TRUE, cook.levels = c(0.5, 1), add.smooth = getOption("add.smooth"), label.pos = c(4, 2), cex.caption = 1)

`x` |
a |

`which` |
a subset of the numbers 1:5 specifying which plots to produce (out of those listed in Description section). |

`caption` |
captions to appear above the plots. |

`panel` |
panel function. The useful alternative to |

`sub.caption` |
common title - above figures if there are
multiple; used as |

`main` |
title to each plot - in addition to the above |

`ask` |
logical; if |

`...` |
other parameters to be passed through to plotting functions. |

`id.n` |
number of points to be labelled in each plot starting with the most extreme. |

`labels.id` |
vector of labels, from which the labels for extreme
points will be chosen. |

`cex.id` |
magnification of point labels. |

`qqline` |
logical indicating if a |

`cook.levels` |
levels of Cook's distance at which to draw contours. |

`add.smooth` |
logical indicating if a smoother should be added to
most plots; see also |

`label.pos` |
positioning of labels, for the left half and right half of the graph respectively, for plots 1-3. |

`cex.caption` |
controls the size of 'caption'. |

`sub.caption`

- by default the function call - is shown as a subtitle
(under the x-axis title) on each plot when plots are on separate
pages, or as a subtitle in the outer margin (if any) when there
are multiple plots per page.

The "Scale-Location" plot, also called "Spread-Location" or "S-L"
plot, takes the square root of the absolute residuals in order to
diminish skewness (*sqrt{| E |}* is much less skewed
than *| E |* for Gaussian zero-mean *E*).

The S-L, the Q-Q, and the Residual-Leverage plot, use
*standardized* residuals which have identical variance (under the
hypothesis). They are given as *R[i]
/ (s*sqrt(1 - h.ii))* where *h.ii* are the diagonal
entries of the hat matrix, `influence()$hat`

, see also
`hat`

.

The Residual-Leverage plot shows contours of equal Cook's
distance, for values of `cook.levels`

(by default 0.5 and 1) and
omits cases with leverage one. If the leverages are constant, as
typically in a balanced `aov`

situation, the plot uses factor
level combinations instead of the leverages for the x-axis.

Modification of `plot.lm`

by the R Core Team. Adapted
for `"gnm"`

objects by Heather Turner.

`gnm`

, `plot.lm`

set.seed(1) ## Fit an association model with homogeneous row-column effects RChomog <- gnm(Freq ~ origin + destination + Diag(origin, destination) + MultHomog(origin, destination), family = poisson, data = occupationalStatus) ## Plot model diagnostics plot(RChomog) ## Put 4 plots on 1 page; allow room for printing model formula in outer margin: par(mfrow = c(2, 2), oma = c(0, 0, 3, 0)) title <- paste(deparse(RChomog$formula, width.cutoff = 50), collapse = "\n") plot(RChomog, sub.caption = title) ## Fit smoother curves plot(RChomog, sub.caption = title, panel = panel.smooth) plot(RChomog, sub.caption = title, panel = function(x,y) panel.smooth(x, y, span = 1))

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