The intracluster correlation coefficient (rho) provides a measure of similarity within clusters.
*type* = 1 is defined to be the Pearson correlation coefficient for NM(M-1)pairs (yij,yik) for i
between 1 and N and j<>k (see Lohr (1999: p. 139). The average cluster size is used as the equal cluster
size quantity in Equation 5.8 of Lohr (1999). If the clusters are perfectly homogeneous (total variation is all
between-cluster variability), then ICC=1.

*type* = 2 is the adjusted r-square, an alternative quantity following Equation 5.10 in Lohr (1999). It is the
relative amount of variability in the population explained by the cluster means, adjusted for the number
of degrees of freedom. If the clusters are homogeneous, then the cluster means are highly variable relative
to variation within clusters, and the r-square will be high.

*type* = 3 is calculated using one-way random effects models (Donner, 1986).
The formula is

rho = (BMS-WMS)/(BMS+(m-1)*WMS)

where BMS is the mean square between clusters, WMS is the mean square within clusters and m is the
adjusted mean cluster size for clusters with unequal sample size. All clusters with zero elementary
units should be deleted before calculation. *type* = 3 can be used with binary data
(Ridout et al. 1999)

If *est*=1, the boostrap mean (value), variance of the mean and 0.025 and 0.975 percentiles are outputted.