Diagnostic plots for assessing the normality of residuals and random
effects in the linear mixed-effects fit are obtained. The
form argument gives considerable flexibility in the type of
plot specification. A conditioning expression (on the right side of a
| operator) always implies that different panels are used for
each level of the conditioning factor, according to a Trellis
display.
# S3 method for lme
qqnorm(y, form, abline, id, idLabels, grid, …)an optional one-sided formula specifying the desired type of
plot. Any variable present in the original data frame used to obtain
y can be referenced. In addition, y itself
can be referenced in the formula using the symbol
".". Conditional expressions on the right of a |
operator can be used to define separate panels in a Trellis
display. The expression on the right hand side of form and to
the left of a | operator must evaluate to a residuals vector,
or a random effects matrix. Default is ~ resid(., type = "p"),
corresponding to a normal plot of the standardized residuals
evaluated at the innermost level of nesting.
an optional numeric value, or numeric vector of length two. If given as a single value, a horizontal line will be added to the plot at that coordinate; else, if given as a vector, its values are used as the intercept and slope for a line added to the plot. If missing, no lines are added to the plot.
an optional numeric value, or one-sided formula. If given as
a value, it is used as a significance level for a two-sided outlier
test for the standardized residuals (random effects). Observations with
absolute standardized residuals (random effects) greater than the
\(1 - value/2\) quantile of the standard normal distribution are
identified in the plot using idLabels. If given as a one-sided
formula, its right hand side must evaluate to a logical, integer, or
character vector which is used to identify observations in the
plot. If missing, no observations are identified.
an optional vector, or one-sided formula. If given as a
vector, it is converted to character and used to label the
observations identified according to id. If given as a
one-sided formula, its right hand side must evaluate to a vector
which is converted to character and used to label the identified
observations. Default is the innermost grouping factor.
an optional logical value indicating whether a grid should
be added to plot. Default is FALSE.
optional arguments passed to the Trellis plot function.
a diagnostic Trellis plot for assessing normality of residuals or random effects.
# NOT RUN {
fm1 <- lme(distance ~ age, Orthodont, random = ~ age | Subject)
## normal plot of standardized residuals by gender
qqnorm(fm1, ~ resid(., type = "p") | Sex, abline = c(0, 1))
## normal plots of random effects
qqnorm(fm1, ~ranef(.))
# }
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