n4means               package:epibasix               R Documentation

_N_u_m_b_e_r _o_f _S_u_b_j_e_c_t_s _R_e_q_u_i_r_e_d _f_o_r _a _R_a_n_d_o_m_i_z_e_d _T_r_i_a_l _w_i_t_h _a _C_o_n_t_i_n_u_o_u_s _O_u_t_c_o_m_e

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

     This function provides detailed sample size estimation information
     to determine the number of subjects that must be enrolled in a
     randomized trial with a continuous outcome.

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

     n4means(delta, sigma, alpha=0.05, power=0.8, AR=1, two.tailed=TRUE, digits=3)

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

   delta: The minimum detectable difference between population means.

   sigma: The standard error of the outcome.

      AR: The Allocation Ratio: One implies an equal number of subjects
          per treatment and control group (maximum efficiency), > 1,
          implies more subjects will be enrolled in the control group 
          (e.g. in the case of costly intervention), < 1 implies more
          in the tretment group (rarely used).

   alpha: The desired Type I Error Rate

   power: The desired level of power, recall power = 1 - Type II Error.

two.tailed: Logical, If TRUE calculations are based on a two-tailed
          Type I error, if FALSE, a one-sided calculation is performed.

  digits: Number of Digits to round calculations

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

     This function provides detailed information, similar to PROC POWER
     in SAS, but with less functionality and more concise output.  It
     is used for sample size estimation in  a randomized trial where
     the outcome is continuous, such as blood pressure, or weight.

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

      nE: The minimum number of subjects required in the Experimental
          group.

      nC: The minimum number of subjects required in the Control group.

   delta: The minimum detectable difference between population means.

   sigma: The standard error of the outcome.

   alpha: The desired Type I Error Rate

   power: The desired level of power, recall power = 1 - Type II Error.

      AR: The Allocation Ratio

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

     Michael Rotondi, mrotondi@uwo.ca

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

     Matthews JNS.  Introduction to Randomized Controlled Clinical
     Trials (2nd Ed.) Chapman & Hall: New York, 2006.

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

     'n4props'

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

     ## Not run: 
     Suppose we wish to test whether a blood pressure medication reduces diastolic blood
     pressure by 10 mm Hg, at standard significance and power, assume the standard deviation is 10 mm Hg.
     ## End(Not run)
     n4means(delta=10, sigma=10, alpha=0.05, power=0.80);

