**cv.lm() function is defined under the DAAG package which is used for k-fold validation.**

Description. This **function** gives internal and cross-validation measures of predictive accuracy for ordinary linear regression. The data are randomly assigned to a number of `folds’. Each fold is removed, in turn, while the remaining data is used to re-fit the regression model and to predict at the deleted observations.

## Description

This function gives internal and cross-validation measures of predictive accuracy for ordinary linear regression. The data are randomly assigned to a number of `folds’. Each fold is removed, in turn, while the remaining data is used to re-fit the regression model and to predict at the deleted observations.

## Usage

**cv.lm(df = houseprices, form.lm = formula(sale.price ~ area), m=3, dots = FALSE, seed=29, plotit=TRUE, printit=TRUE)**

## Arguments

df

a data frame

form.lm

a formula object

m

the number of folds

dots

uses pch=16 for the plotting character

seed

random number generator seed

plotit

if TRUE, a plot is constructed on the active device

printit

if TRUE, output is printed to the screen

## Value

- ssthe cross-validation residual sum of squares
- dfdegrees of freedom