Fits a generalized linear model with empirical likelihood.

## Usage

```
el_glm(
formula,
family = gaussian,
data,
weights = NULL,
na.action,
start = NULL,
etastart = NULL,
mustart = NULL,
offset,
control = el_control(),
...
)
```

## Arguments

- formula
An object of class

`formula`

(or one that can be coerced to that class): a symbolic description of the model to be fitted.- family
A description of the error distribution and link function to be used in the model. Only the result of a call to a family function is supported. See ‘Details’.

- data
An optional data frame, list or environment (or object coercible by

`as.data.frame()`

to a data frame) containing the variables in the formula. If not found in data, the variables are taken from`environment(formula)`

.- weights
An optional numeric vector of weights to be used in the fitting process. Defaults to

`NULL`

, corresponding to identical weights. If non-`NULL`

, weighted empirical likelihood is computed.- na.action
A function which indicates what should happen when the data contain

`NA`

s. The default is set by the`na.action`

setting of`options`

, and is`na.fail`

if that is unset.- start
Starting values for the parameters in the linear predictor. Defaults to

`NULL`

and is passed to`glm.fit()`

.- etastart
Starting values for the linear predictor. Defaults to

`NULL`

and is passed to`glm.fit()`

.- mustart
Starting values for the vector of means. Defaults to

`NULL`

and is passed to`glm.fit()`

.- offset
An optional expression for specifying an

*a priori*known component to be included in the linear predictor during fitting. This should be`NULL`

or a numeric vector or matrix of extents matching those of the response. One or more`offset`

terms can be included in the formula instead or as well, and if more than one are specified their sum is used.- control
An object of class ControlEL constructed by

`el_control()`

.- ...
Additional arguments to be passed to

`glm.control()`

.

## Value

An object of class of GLM.

## Details

Suppose that we observe \(n\) independent random variables \({Z_i} \equiv {(X_i, Y_i)}\) from a common distribution, where \(X_i\) is the \(p\)-dimensional covariate (including the intercept if any) and \(Y_i\) is the response. A generalized linear model specifies that \({\textrm{E}(Y_i | X_i)} = {\mu_i}\), \({G(\mu_i)} = {X_i^\top \theta}\), and \({\textrm{Var}(Y_i | X_i)} = {\phi V(\mu_i)}\), where \(\theta = (\theta_0, \dots, \theta_{p-1})\) is an unknown \(p\)-dimensional parameter, \(\phi\) is an optional dispersion parameter, \(G\) is a known smooth link function, and \(V\) is a known variance function.

With \(H\) denoting the inverse link function, define the quasi-score
$${g_1(Z_i, \theta)} =
\left\{
H^\prime(X_i^\top \theta) \left(Y_i - H(X_i^\top \theta)\right) /
\left(\phi V\left(H(X_i^\top \theta)\right)\right)
\right\}
X_i.$$
Then we have the estimating equations
\(\sum_{i = 1}^n g_1(Z_i, \theta) = 0\).
When \(\phi\) is known, the (profile) empirical likelihood ratio for a
given \(\theta\) is defined by
$$R_1(\theta) =
\max_{p_i}\left\{\prod_{i = 1}^n np_i :
\sum_{i = 1}^n p_i g_1(Z_i, \theta) = 0,\
p_i \geq 0,\
\sum_{i = 1}^n p_i = 1
\right\}.$$
With unknown \(\phi\), we introduce another estimating function based on
the squared residuals. Let \({\eta} = {(\theta, \phi)}\) and
$${g_2(Z_i, \eta)} =
\left(Y_i - H(X_i^\top \theta)\right)^2 /
\left(\phi^2 V\left(H(X_i^\top \theta)\right)\right) - 1 / \phi.$$
Now the empirical likelihood ratio is defined by
$$R_2(\eta) =
\max_{p_i}\left\{\prod_{i = 1}^n np_i :
\sum_{i = 1}^n p_i g_1(Z_i, \eta) = 0,\
\sum_{i = 1}^n p_i g_2(Z_i, \eta) = 0,\
p_i \geq 0,\
\sum_{i = 1}^n p_i = 1
\right\}.$$
`el_glm()`

first computes the parameter estimates by calling `glm.fit()`

(with `...`

if any) with the `model.frame`

and `model.matrix`

obtained from
the `formula`

. Note that the maximum empirical likelihood estimator is the
same as the the quasi-maximum likelihood estimator in our model. Next, it
tests hypotheses based on asymptotic chi-square distributions of the
empirical likelihood ratio statistics. Included in the tests are overall
test with
$$H_0: \theta_1 = \theta_2 = \cdots = \theta_{p-1} = 0,$$
and significance tests for each parameter with
$$H_{0j}: \theta_j = 0,\ j = 0, \dots, p-1.$$

The available families and link functions are as follows:

`gaussian`

:`"identity"`

,`"log"`

, and`"inverse"`

.`binomial`

:`"logit"`

,`"probit"`

, and`"log"`

.`poisson`

:`"log"`

,`"identity"`

, and`"sqrt"`

.`quasipoisson`

:`"log"`

,`"identity"`

, and`"sqrt"`

.

## References

Chen SX, Cui H (2003).
``An Extended Empirical Likelihood for Generalized Linear Models.''
*Statistica Sinica*, **13**(1), 69--81.

Kolaczyk ED (1994).
``Empirical Likelihood for Generalized Linear Models.''
*Statistica Sinica*, **4**(1), 199--218.

## See also

EL, GLM, `el_lm()`

, `elt()`

,
`el_control()`

## Examples

```
data("warpbreaks")
fit <- el_glm(wool ~ .,
family = binomial, data = warpbreaks, weights = NULL, na.action = na.omit,
start = NULL, etastart = NULL, mustart = NULL, offset = NULL
)
summary(fit)
#>
#> Empirical Likelihood
#>
#> Model: glm (binomial family with logit link)
#>
#> Call:
#> el_glm(formula = wool ~ ., family = binomial, data = warpbreaks,
#> weights = NULL, na.action = na.omit, start = NULL, etastart = NULL,
#> mustart = NULL, offset = NULL)
#>
#> Number of observations: 54
#> Number of parameters: 4
#>
#> Parameter values under the null hypothesis:
#> (Intercept) breaks tensionM tensionH
#> 6.337e-08 0.000e+00 0.000e+00 0.000e+00
#>
#> Lagrange multipliers:
#> [1] 1.81250 -0.05261 -0.41072 -0.71437
#>
#> Maximum EL estimates:
#> (Intercept) breaks tensionM tensionH
#> 1.67965 -0.04677 -0.44662 -0.67062
#>
#> logL: -217.4 , logLR: -1.97
#> Chisq: 3.94, df: 3, Pr(>Chisq): 0.268
#> Constrained EL: converged
#>
#> Coefficients:
#> Estimate Chisq Pr(>Chisq)
#> (Intercept) 1.67965 6.226 0.0126 *
#> breaks -0.04677 3.941 0.0471 *
#> tensionM -0.44662 0.568 0.4511
#> tensionH -0.67062 1.628 0.2020
#> ---
#> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#>
#> Dispersion for binomial family: 1
#>
```