glmm.admb package:glmmADMB R Documentation
_G_e_n_e_r_a_l_i_z_e_d _L_i_n_e_a_r _M_i_x_e_d _M_o_d_e_l_s _u_s_i_n_g _A_D _M_o_d_e_l _B_u_i_l_d_e_r
_D_e_s_c_r_i_p_t_i_o_n:
Fits mixed-effects models to count data using Binomial, Poisson or
negative binomial response distributions. Zero-inflated versions
of Poisson and negative binomial distributions are available.
_U_s_a_g_e:
glmm.admb(fixed, random, group, data, family = "poisson", link, corStruct = "diag",
impSamp = 0, easyFlag = TRUE, zeroInflation = FALSE, imaxfn = 10, save.dir= NULL)
_A_r_g_u_m_e_n_t_s:
fixed: a two-sided linear formula object describing the
fixed-effects part of the model, with the response on the
left of a '~' operator and the terms, separated by '+'
operators, on the right.
random: optionally, a one-sided formula object describing the
random-effects part of the model. When 'random' is missing an
ordinary GLM without random effects is fitted.
group: a character string naming the main nesting variable.
data: a data frame containing the variables named in 'fixed',
'random' and 'group'.
family: a character string determining the response distribution:
"poisson" or "nbinom".
link: a character string specifying the shape of the link function
("logit" or "probit") used for the "binomial" family.
corStruct: a character string specifying the covariance structure of
the random effects vector. Two types of covariance matrices
are are currently implemented: "diag" (diagonal matrix) and
"full" (positive definite matrix with all elements being
estimated).
impSamp: integer. The sample size in the importance sampling
correction of the Laplace approximation (impSamp=0 yields a
plain Laplace approximation).
easyFlag: logical. If 'TRUE', a faster but less robust optimization
algorithm is employed (only "poisson" and "nbinom").
zeroInflation: logical. If 'TRUE', a zero-inflated model is fitted
(only "poisson" and "nbinom")
imaxfn: integer. Number of function evaluations used in intermediate
optimization steps.
save.dir: If a quoted directory name is specified all the ADMB output
files are saved there.
_D_e_t_a_i_l_s:
Currently, the "binomial" familiy only accepts Bernoully responce
(0 or 1).
Parameterization of the negative binomial distribution: Var(Y) =
E(Y)*(1+E(Y)/alpha).
Zero-inflation: With probability '1-pz' Y comes from a Poisson (or
negative binomial) distribution, and with probability 'pz' Y is
zero (Bohning et al., 1999). Only available with "poisson" and
"nbinom" response.
Parameters are estimated by maximum likelihood using the Laplace
approximation to evaluate the marginal likelihood. When 'impSamp
> 0' importance sampling is used to improve the Laplace
approximation (Skaug and Fournier, 2005).
If the message 'Proper convergence could not be reached' occurs,
try to increase the parameter 'imaxfn' and to set 'easyFlag =
FALSE'.
_V_a_l_u_e:
An object of class 'glmm.admb' representing the model fit. The
generic function 'print' has a method to show the results of the
fit.
b: vector of fixed effects
S: covariance matrix of random effects
alpha: parameter in negative binomial distribution (only when
'family = "poisson"')
pz: Zero-inflation parameter (only when 'zeroInflation = TRUE')
_A_u_t_h_o_r(_s):
H. Skaug skaug@mi.uib.no, David Fournier otter@otter-rsch.com and
Anders Nielsen andersn@hawaii.edu
_R_e_f_e_r_e_n_c_e_s:
Bohning, D. et al (1999). The Zero-Inflated Poisson Model and the
Decayed, Missing and Filled Teeth Index in Dental Epidemiology.
Journal of the Royal Statistical Society. Series A (Statistics in
Society) Vol. 162, No. 2 (1999), pp. 195-209.
Skaug and Fournier (2005). Automatic Evaluation of the Marginal
Likelihood in Nonlinear Hierarchical Models. Unpublished available
from: http://bemata.imr.no/laplace.pdf
_E_x_a_m_p_l_e_s:
data(epil2)
glmm.admb(y~Base*trt+Age+Visit,random=~Visit,group="subject",data=epil2,family="nbinom")