alpha                package:epicalc                R Documentation

_C_r_o_n_b_a_c_h'_s _a_l_p_h_a

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

     Calculate reliability coefficient of items in a data frame

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

     alpha (vars, dataFrame = .data, casewise = FALSE, reverse = TRUE, 
         decimal = 4, vars.to.reverse = NULL, var.labels = TRUE)   

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

    vars: a vector containing at least three variables from the data
          frame

dataFrame: data frame where items are set as variables

casewise: whether on records with completed data on vars will be used

 reverse: whether item(s) negatively correlated with other majority
          will be reversed

 decimal: number of decimal places displayed

var.labels: presence of descriptions of variables on the last column of
          output

vars.to.reverse: variable(s) to reverse

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

     This function is based on the 'reliability' function from package
     'Rcmdr', which computes Cronbach's alpha for a composite scale. 

     There must be at least three items in 'vars' specified by names of
     the variables or their index.

     The argument 'reverse' (default = TRUE) automatically reverses
     items negatively correlated with other majority into negative and
     reports the activities in the first column of the last result
     section. This is however overwritten by the argument
     'vars.to.reverse'

     Similar to the 'reliability' function, users can see the effect of
     removing each item on the coefficents and the item-rest
     correlation.

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

     Virasakdi Chongsuvivatwong <cvirasak@medicine.psu.ac.th>

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

     'cronbach' from 'psy' package and 'reliability' from 'Rcmdr'
     package and 'tableStack' and 'unclassDataframe' of Epicalc

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

     data(Cars93, package="MASS")
     use(Cars93)
     alpha(vars=c(Min.Price:MPG.highway, EngineSize))

     data(Attitudes)
     use(Attitudes)

     ## Please use full screen of Rconsole
     ## for better display of the labels.
     alpha(qa1:qa18)
     alpha(qa1:qa18, reverse=FALSE)

