envrtest               package:labdsv               R Documentation

_E_n_v_i_r_o_n_m_e_n_t_a_l _D_i_s_t_r_i_b_u_t_i_o_n _T_e_s_t

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

     Calculates whether the value of a specified environmental variable
     has an improbable distribution with respect to a specified vector

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

     envrtest(set,env,numitr=1000,minval=0,replace=FALSE,
          plotit = TRUE, main = paste(deparse(substitute(set)),
          " on ", deparse(substitute(env))))

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

     set: a vector of logical or quantitative values

     env: the quantitative variable whose distribution is to be tested

  numitr: the number of randomizations to iterate to calculate
          probabilities

  minval: the threshold to use to partition the data into a logical  if
          set is quantitative

 replace: whether to permute (replace=FALSE) or bootstrap
          (replace=TRUE) the values in the permutation test

  plotit: logical; plot results if TRUE

    main: title for plot if plotted

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

     Calculates the maximum within-set difference in the values of
     vector env, and the distribution of the permuted random within-set
     differences.  It then plots the observed difference as a red line,
     and the sorted permuted differences and prints the probability of
     getting such a limited distribution. The probability is calculated
     by permuting numitr-1 times, counting the number of times the
     permuted maximum difference is as small or smaller than observed
     (n), and calculating (n+1)/numitr.  To get three-digit
     probabilities, set numitr=1000 (the default)

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

     Produces a plot on the current graphics device, and an invisible
     list with the components observed within-set difference and the
     p-value.

_N_o_t_e:

     The plot is based on the concept of constraint, or limiting value,
     and checks to see whether the distribution of a particular
     variable within a cluster is constrained in an improbable way.

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

     David W. Roberts droberts@montana.edu <URL:
     http://ecology.msu.montana.edu/droberts>

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

     <URL: http://ecology.msu.montana.edu/labdsv/R>

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

         data(bryceveg) # returns a vegetation data.frame
         data(brycesite) # returns and environmental data.frame
         envrtest(bryceveg$berrep>0,brycesite$elev)

