power.anova.test            package:stats            R Documentation

_P_o_w_e_r _c_a_l_c_u_l_a_t_i_o_n_s _f_o_r _b_a_l_a_n_c_e_d _o_n_e-_w_a_y _a_n_a_l_y_s_i_s _o_f _v_a_r_i_a_n_c_e _t_e_s_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     Compute power of test or determine parameters to obtain target
     power.

_U_s_a_g_e:

     power.anova.test(groups = NULL, n = NULL, between.var = NULL,
                      within.var = NULL, sig.level = 0.05, power = NULL)

_A_r_g_u_m_e_n_t_s:

  groups: Number of groups

       n: Number of observations (per group)

between.var: Between group variance

within.var: Within group variance

sig.level: Significance level (Type I error probability)

   power: Power of test (1 minus Type II error probability)

_D_e_t_a_i_l_s:

     Exactly one of the parameters 'groups', 'n', 'between.var',
     'power', 'within.var', and 'sig.level' must be passed as NULL, and
     that parameter is determined from the others. Notice that
     'sig.level' has non-NULL default so NULL must be explicitly passed
     if you want it computed.

_V_a_l_u_e:

     Object of class '"power.htest"', a list of the arguments
     (including the computed one) augmented with 'method' and 'note'
     elements.

_N_o_t_e:

     'uniroot' is used to solve power equation for unknowns, so you may
     see errors from it, notably about inability to bracket the root
     when invalid arguments are given.

_A_u_t_h_o_r(_s):

     Claus Ekstrom

_S_e_e _A_l_s_o:

     'anova', 'lm', 'uniroot'

_E_x_a_m_p_l_e_s:

     power.anova.test(groups=4, n=5, between.var=1, within.var=3)
     # Power = 0.3535594

     power.anova.test(groups=4, between.var=1, within.var=3,
                      power=.80)
     # n = 11.92613

     ## Assume we have prior knowledge of the group means:
     groupmeans <- c(120, 130, 140, 150)
     power.anova.test(groups = length(groupmeans),
                      between.var=var(groupmeans),
                      within.var=500, power=.90) # n = 15.18834

