EZ2                   package:EZ2                   R Documentation

_F_i_t _d_i_f_f_u_s_i_o_n _m_o_d_e_l _t_o _o_b_s_e_r_v_e_d _s_a_m_p_l_e _m_o_m_e_n_t_s

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

     Fit the a simplified diffusion model for response time and
     accuracy to observed proportions of errors and response time means
     and variances.

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

     EZ2(pstart, ObsValPair, ..., method = "Nelder-Mead", control = list(), hessian = FALSE)

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

  pstart: Vector with named starting parameter values 

ObsValPair: Observed-predicted value pair in the form '0.80 ~
          EZ2.pe(v1, z, a) ' or 'vrt2 ~ EZ2.pe(v2, a-z, a) if vrt2
          exists in the global environment and is numeric ' 

     ...: More Observed-predicted value pairs (as many as desired, see
          example) 

  method: See 'method' parameter of 'optim'. 

 control: See 'control' parameter of 'optim'. 

 hessian: See 'hessian' parameter of 'optim'. 

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

     EZ2 fits a simplified version of the diffusion model for human and
     monkey response times  and accuracy to the means and variances of
     the observables. This model of information accumulation and
     decision is a simplified version of Ratcliff's diffusion model
     (1978). 

     Use 'EZ2batch' for more user friendly fitting automatically each
     row in a 'data.frame'.

_V_a_l_u_e:

     The list returned by optim. This list contains 

     par: A vector containing the estimates

   value: Sum of squared prediction errors. This should be very close
          to zero (order of '1e-8') if there are as many
          observed-predicted moment value pairs as there are unknown
          parameters (the estimates then constitute method of moments
          estimators).

     For other list members, see 'Value' section of 'optim' for a
     complete description.

_N_o_t_e:

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

     Raoul Grasman

_R_e_f_e_r_e_n_c_e_s:

     Ratcliff. Theory of Memory Retrieval. Psychological review (1978)
     vol. 85 (2) pp. 59-108 

     Grasman et al. EZ2: An extension of teh EZ-diffusion model for
     Response Time and Accuracy. Journal of Mathematical Psychology
     (2007) submitted

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

     'EZ2-package', 'EZ2batch'

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

      Vrt0 <- EZ2.vrt(0.1, 0.08, 0.12)
       Pe0 <- EZ2.pe(0.1, 0.08, 0.12)
      Vrt1 <- EZ2.vrt(0.15, 0.12-0.08, 0.12)
       Pe1 <- EZ2.pe(0.15, 0.12-0.08, 0.12)
       
      EZ2(c(v0=.156,v1=.0844,z=.0631,a=.1263), 
      Vrt0 ~ EZ2.vrt(v0,z,a), 
       Pe0 ~ EZ2.pe(v0,z,a), 
      Vrt1 ~ EZ2.vrt(v1,a-z,a), 
       Pe1 ~ EZ2.pe(v1, a-z, a))

