poisgof               package:epicalc               R Documentation

_G_o_o_d_n_e_s_s _o_f _f_i_t _t_e_s_t _f_o_r _m_o_d_e_l_i_n_g _o_f _c_o_u_n_t _d_a_t_a

_D_e_s_c_r_i_p_t_i_o_n:

     Poisson and negative binomial regression are used for modeling
     count data. The command tests the deviance against degrees of
     freedom in the model determining whether there is overdispersion.

_U_s_a_g_e:

     poisgof (model)

_A_r_g_u_m_e_n_t_s:

   model: A Poisson or negative binomial model

_D_e_t_a_i_l_s:

     To test the significance of overdispersion of the errors of a
     Poisson or negative binomial model, the deviance is test against
     degrees of freedom using chi-squared distribution. A low P value
     indicates significant overdispersion.

_A_u_t_h_o_r(_s):

     Virasakdi Chongsuvivatwong <cvirasak@medicine.psu.ac.th>

_S_e_e _A_l_s_o:

     `glm'

_E_x_a_m_p_l_e_s:

     library(MASS)
     quine.pois <- glm(Days ~ Sex/(Age + Eth*Lrn), data = quine, family=poisson)
     poisgof(quine.pois)
     quine.nb1 <- glm.nb(Days ~ Sex/(Age + Eth*Lrn), data = quine)
     poisgof(quine.nb1)

