# Boot

##### Bootstrapping for regression models

This function provides a simple front-end to the `boot`

function in the
package also called `boot`

. Whereas `boot`

is very general and therefore
has many arguments, the `Boot`

function has very few arguments, but should
meet the needs of many users.

- Keywords
- regression

##### Usage

```
## S3 method for class 'default':
Boot(object, f=coef, labels=names(coef(object)),
R=999, method=c("case", "residual"))
## S3 method for class 'lm':
Boot(object, f=coef, labels=names(coef(object)),
R=999, method=c("case", "residual"))
## S3 method for class 'glm':
Boot(object, f=coef, labels=names(coef(object)),
R=999, method=c("case", "residual"))
## S3 method for class 'nls':
Boot(object, f=coef, labels=names(coef(object)),
R=999, method=c("case", "residual"))
```

##### Arguments

- object
- A regression object of class
`lm`

,`glm`

or`nls`

. The function may work with other regression objects that support the`update`

method and have a`subset`

argument - f
- A function whose one argument is the name of a regression object that will be applied to the updated regression object to
compute the statistics of interest. The default is
`coef`

, to return to regression coefficient estimates. For example, - labels
- Provides labels for the statistics computed by
`f`

. If this argument is of the wrong length, then generic labels will be generated. - R
- Number of bootstrap samples. The number of bootstrap samples actually computed may be smaller than
this value if either the fitting method is iterative, or if the rank of a fittle
`lm`

or`glm`

model is different in the bootstrap - method
- The bootstrap method, either
case for resampling cases orresiduals for a residual bootstrap. See the details below. The residual bootstrap is available only for`lm`

and`nls`

objects and will re

##### Details

Whereas the `boot`

function is
very general, `Boot`

is very specific. It takes the information from a
regression object and the choice of `method`

, and creates a function that is
passed as the `statistic`

argument to `boot`

. The argument `R`

is also passed to `boot`

. All other arguments to `boot`

are
kept at their default values.
The methods available for `lm`

and `nls`

objects are `nls`

objects ordinary residuals are used
in the resampling rather than the standardized residuals used in the `lm`

method. The residual bootstrap for
generalized linear models has several competing approaches, but none are
without problems. If you want to do a residual bootstrap for a glm, you
will need to write your own call to `boot`

.
An attempt to model fit to a bootstrap sample may fail. In a `lm`

or
`glm`

fit, the bootstrap sample could have a different rank from the original
fit. In an `nls`

fit, convergence may not be obtained for some bootstraps.
In either case, `NA`

are returned for the value of the function `f`

.
The summary methods handle the `NA`

s appropriately.

##### Value

- See
`boot`

for the returned value from this function. The car package includes additional generic functions summary, confint and hist that works with boot objects.

##### References

Davison, A, and Hinkley, D. (1997) *Bootstrap Methods and their
Applications*. Oxford: Oxford University Press.
Fox, J. and Weisberg, S. (2011) *Companion to Applied Regression*, Second Edition.
Thousand Oaks: Sage.
Fox, J. and Weisberg, S. (2012) *Bootstrapping*,
*Applied Linear Regression*, Fourth Edition, Wiley
Wiley, Chapters 4 and 11.

##### See Also

Functions that work with
`Boot`

objects from the `boot`

package are
`boot.array`

,
`boot.ci`

,
`plot.boot`

and
`empinf`

. Additional
functions in the `car`

package are
`summary.boot`

,
`confint.boot`

, and
`hist.boot`

.

##### Examples

```
m1 <- lm(Fertility ~ ., swiss)
betahat.boot <- Boot(m1, R=199) # 199 bootstrap samples--too small to be useful
summary(betahat.boot) # default summary
confint(betahat.boot)
hist(betahat.boot)
# Bootstrap for the estimated residual standard deviation:
sigmahat.boot <- Boot(m1, R=199, f=sigmaHat, labels="sigmaHat")
summary(sigmahat.boot)
confint(sigmahat.boot)
```

*Documentation reproduced from package car, version 2.0-20, License: GPL (>= 2)*