exactmatch              package:MatchIt              R Documentation

_E_x_a_c_t _m_a_t_c_h_i_n_g

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

     'exactmatch' is a sub-function of 'matchit' that does exact
     matching on the set of covariates.

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

     exactmatch <- exactmatch(formula, data, counter=TRUE)

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

 formula: (required).  Takes the form of 'T ~ X1 + X2', where 'T' is a
          binary treatment indicator and 'X1' and 'X2' are the
          pre-treatment covariates, and 'T', 'X1', and 'X2' are
          contained in the same data frame.  Exact matching is done on
          the variables on the right-hand side of 'formula'.

    data: (required).  Data frame containing the variables called in
          the 'formula'.   The dataframe should not include variables
          with the names 'psclass', 'psweights', or 'pscore', as these
          are expressly reserved in the output dataframe for MatchIt.

 counter: Whether to display counter indicating the progress of the
          matching (default=TRUE).

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

     This sub-function is called automatically by the 'matchit' command
     when 'exact=TRUE' is chosen, meaning exact matching on all
     covariates in the assignment model.   It creates subclasses
     defined by the values of the covariates, where each subclass must
     contain some treated and some control units.  Units with no exact
     matches in the other treatment group are discarded.  This function
     is called directly by 'matchit' and does not generally need to be
     called directly by users; these details are included for advanced
     users.

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

 psclass: Subclass index in an ordinal scale from 1 to the number of
          subclasses.   Unmatched units have subclass=0.  With exact
          matching, these subclasses are defined by the categories of
          the variables in 'formula'.

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

     Daniel Ho <deho@fas.harvard.edu>;  Kosuke Imai
     <kimai@princeton.edu>; Gary King <king@harvard.edu>; Elizabeth
     Stuart<stuart@stat.harvard.edu>

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

     Please use 'help.matchit' to access the matchit reference manual. 
     The complete document is available online at <URL:
     http://gking.harvard.edu/matchit>.

