# lm.case

##### case statistics for regression analysis

Case statistics for regression analysis.
`case.lm`

calculates the statistics.
`plot.case`

plots the cases, one statistic per panel, and
illustrates and flags all observations for which the standard
thresholds are exceeded. `plot.case`

returns an object with
class `c("trellis.case", "trellis")`

containing the plot and the row.names of the
flagged observations. The object is printed by a method which
displays the set of graphs and prints the list of flagged cases.
`panel.case`

is a panel function for `plot.case`

.

- Keywords
- hplot, regression

##### Usage

```
case(fit, ...)
## S3 method for class 'lm':
case(fit, lms = summary.lm(fit), lmi = lm.influence(fit), ...)
## S3 method for class 'case':
plot(x, fit,
which=c("stu.res","si","h","cook","dffits",
dimnames(x)[[2]][-(1:8)]), ##DFBETAS
between.in=list(y=4, x=9),
cex.threshold=1.2,
main.in=list(
paste(deparse(fit$call), collapse=""),
cex=main.cex),
sigma.in=summary.lm(fit)$sigma,
p.in=summary.lm(fit)$df[1]-1,
main.cex=NULL,
...)
panel.case(x, y, subscripts, rownames, group.names,
thresh, case.large,
nn, pp, ss, cex.threshold,
...)
```

##### Arguments

- fit
`"lm"`

object computed with`x=TRUE`

- lms
`summary.lm(fit)`

- lmi
`lm.influence(fit)`

- x
- In
`plot.case`

, the matrix output from`case.lm`

containing case diagnostics on each observation in the original dataset. In`panel.case`

, the x variable to be plotted - which
- In
`plot.case`

, the names of the columns of x that are to be graphed. - between.in
`between`

trellis/lattice argument.- cex.threshold
- Multiplier for
`cex`

for the threshold values. - main.in
`main`

title for`xyplot`

. The default main title displays the linear model formula from`fit`

.- sigma.in
- standard error for the
`fit`

. - p.in
- The number of degrees of freedom associated with the fitted model.
- main.cex
`cex`

for main title.- ...
- other arguments to
`xyplot`

- y
- the y variable to be plotted.
- thresh
- Named list of lists. Each list contains the components threshold ($y$-locations where a reference line will be drawn), thresh.label (the right-axis labels for the reference lines), thresh.id (the bounds defining "Noteworthy Observations").
- case.large
- Named list of "Noteworthy Observations".
- nn
- Number of rows in original dataset.
- pp
- The number of degrees of freedom associated with the fitted model.
- ss
- Standard error for the
`fit`

. - subscripts
- trellis/lattice argument, position in the reshaped
dataset constructed by
`plot.case`

before calling`xyplot`

. - rownames
- row name in the original data.frame.
- group.names
- names of the individual statistics.

##### Details

`lm.influence`

is part of S-Plus and R
`case.lm`

and `plot.case`

are based on:
Section 4.3.3 "Influence of Individual Obervations
in Chambers and Hastie", *Statistical Models in S*.

##### Value

`case.lm`

returns a matrix, with one row for each observation in the original dataset. The columns contain the diagnostic statistics:`e`

(residuals),`h`

* (hat diagonals),`si`

* (deleted standard deviation),`sta.res`

(standardized residuals),`stu.res`

* (Studentized deleted resididuals),`dffit`

(difference in fits, change in predicted y when observation i is deleted),`dffits`

* (standardized difference in fits, standardized change in predicted y when observation i is deleted),`cook`

* (Cook's distance), and DFBETAs* (standardized difference in regression coefficients when observation i is deleted, one for each column of the x-matrix, including the intercept).`plot.case`

returns a`c("trellis.case", "trellis")`

object containing the plot (including the starred columns by default) and also retains the row.names of the flagged observations in the`$panel.args.common$case.large`

component. The print method for the`c("trellis.case", "trellis")`

object prints the graph and the list of flagged observations.`panel.case`

is a panel function for`plot.case`

.

##### References

Heiberger, Richard M. and Holland, Burt (2004b).
*Statistical Analysis and Data Display: An Intermediate Course
with Examples in S-Plus, R, and SAS*.
Springer Texts in Statistics. Springer.
ISBN 0-387-40270-5.

##### See Also

##### Examples

```
data(kidney)
kidney2.lm <- lm(clearance ~ concent + age + weight + concent*age,
data=kidney,
na.action=na.exclude) ## recommended
kidney2.case <- case(kidney2.lm)
## this picture looks much better in portrait, specification is device dependent
plot(kidney2.case, kidney2.lm, par.strip.text=list(cex=.9),
layout=c(2,3))
```

*Documentation reproduced from package HH, version 3.1-23, License: GPL (>= 2)*