icc                   package:psy                   R Documentation

_I_n_t_r_a_c_l_a_s_s _c_o_r_r_e_l_a_t_i_o_n _c_o_e_f_f_i_c_i_e_n_t (_I_C_C)

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

     Computes the ICC of several series of measurements, for example in
     an interrater agreement study. Two types of ICC are proposed:
     consistency and agreement.

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

     icc(data)

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

    data: n*p matrix or dataframe, n subjects p raters

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

     Missing data are omitted in a listwise way. The "agreement" ICC is
     the ratio of the subject variance by the sum of the subject
     variance, the rater variance and the residual; it is generally
     prefered. The "consistency" version is the ratio of the subject
     variance by the sum of the subject variance and the residual; it
     may be of interest when estimating the reliability of pre/post
     variations in measurements.

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

     A list with : 

$nb.subjects: number of subjects under study

$nb.raters: number of raters

$subject.variance: subject variance

$rater.variance: rater variance

$residual: residual variance

$icc.consistency: Intra class correlation coefficient, "consistency"
          version

$icc.agreement: Intra class correlation coefficient, "agreement"
          version

_N_o_t_e:

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

     Bruno Falissard

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

     Shrout, P.E., Fleiss, J.L. (1979), Intraclass correlation: uses in
     assessing rater reliability, Psychological Bulletin, 86, 420-428.

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

     data(expsy)
     icc(expsy[,c(12,14,16)])

     library(boot)
     icc.boot <- function(data,x) {icc(data[x,])[[7]]}
     res <- boot(expsy[,c(12,14,16)],icc.boot,1000)
     quantile(res$t,c(0.025,0.975))  # two-sided bootstrapped confidence interval of icc (agreement)

