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 fromenvironment(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
NAs. The default is set by thena.actionsetting ofoptions, and isna.failif that is unset.- start
Starting values for the parameters in the linear predictor. Defaults to
NULLand is passed toglm.fit().- etastart
Starting values for the linear predictor. Defaults to
NULLand is passed toglm.fit().- mustart
Starting values for the vector of means. Defaults to
NULLand is passed toglm.fit().- offset
An optional expression for specifying an a priori known component to be included in the linear predictor during fitting. This should be
NULLor a numeric vector or matrix of extents matching those of the response. One or moreoffsetterms 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
#>