Extract model parameters and their covariance matrix as well as degrees of freedom (if available) from a fitted model.

`modelparm(model, coef., vcov., df, ...)`

An object of class `modelparm`

with elements

- coef
model parameters

- vcov
covariance matrix of model parameters

- df
degrees of freedom

- model
a fitted model, for example an object returned by

`lm`

,`glm`

,`aov`

,`survreg`

,`fixest`

, or`lmer`

etc.- coef.
an accessor function for the model parameters. Alternatively, the vector of coefficients.

- vcov.
an accessor function for the covariance matrix of the model parameters. Alternatively, the covariance matrix directly.

- df
an optional specification of the degrees of freedom to be used in subsequent computations.

- ...
additional arguments, currently ignored.

One can't expect `coef`

and `vcov`

methods
for arbitrary models to
return a vector of \(p\) fixed effects model parameters (`coef`

)
and corresponding \(p \times p\) covariance matrix (`vcov`

).

The `coef.`

and `vcov.`

arguments can be used to define
modified `coef`

or `vcov`

methods for a specific model.
Methods for `lmer`

, `fixest`

,
and `survreg`

objects are available (internally).

For objects inheriting from class `lm`

the degrees of
freedom are determined from `model`

and the corresponding
multivariate t distribution is used by all methods to `glht`

objects. By default, the asymptotic multivariate normal distribution
is used in all other cases unless `df`

is specified by the user.