# addterm.clm2

##### Try all one-term additions to and deletions from a model

Try fitting all models that differ from the current model by adding or deleting a single term from those supplied while maintaining marginality.

- Keywords
- internal

##### Usage

```
# S3 method for clm2
addterm(object, scope, scale = 0, test = c("none", "Chisq"),
k = 2, sorted = FALSE, trace = FALSE,
which = c("location", "scale"), …)
# S3 method for clm2
dropterm(object, scope, scale = 0, test = c("none", "Chisq"),
k = 2, sorted = FALSE, trace = FALSE,
which = c("location", "scale"), …)
```

##### Arguments

- object
A

`clm2`

object.- scope
for

`addterm`

: a formula specifying a maximal model which should include the current one. All additional terms in the maximal model with all marginal terms in the original model are tried. For`dropterm`

: a formula giving terms which might be dropped. By default, the model formula. Only terms that can be dropped and maintain marginality are actually tried.- scale
used in the definition of the AIC statistic for selecting the models. Specifying

`scale`

asserts that the dispersion is known.- test
should the results include a test statistic relative to the original model? The Chisq test is a likelihood-ratio test.

- k
the multiple of the number of degrees of freedom used for the penalty. Only

`k=2`

gives the genuine AIC:`k = log(n)`

is sometimes referred to as BIC or SBC.- sorted
should the results be sorted on the value of AIC?

- trace
if

`TRUE`

additional information may be given on the fits as they are tried.- which
should additions or deletions occur in location or scale models?

- …
arguments passed to or from other methods.

##### Details

The definition of AIC is only up to an additive constant because the likelihood function is only defined up to an additive constant.

##### Value

A table of class `"anova"`

containing columns for the change
in degrees of freedom, AIC and the likelihood ratio statistic. If
`test = "Chisq"`

a column also contains the
p-value from the Chisq test.

##### See Also

##### Examples

```
# NOT RUN {
options(contrasts = c("contr.treatment", "contr.poly"))
if(require(MASS)) { ## dropterm, addterm, housing
mB1 <- clm2(SURENESS ~ PROD + GENDER + SOUPTYPE,
scale = ~ COLD, data = soup, link = "probit",
Hess = FALSE)
dropterm(mB1, test = "Chi") # or
dropterm(mB1, which = "location", test = "Chi")
dropterm(mB1, which = "scale", test = "Chi")
addterm(mB1, scope = ~.^2, test = "Chi", which = "location")
addterm(mB1, scope = ~ . + GENDER + SOUPTYPE,
test = "Chi", which = "scale")
addterm(mB1, scope = ~ . + AGEGROUP + SOUPFREQ,
test = "Chi", which = "location")
## Fit model from polr example:
fm1 <- clm2(Sat ~ Infl + Type + Cont, weights = Freq, data = housing)
addterm(fm1, ~ Infl + Type + Cont, test= "Chisq", which = "scale")
dropterm(fm1, test = "Chisq")
}
# }
```

*Documentation reproduced from package ordinal, version 2019.12-10, License: GPL (>= 2)*