Specifying an intraclass correlation planning value for a conservatively
large sample size requirement is not straightforward with an intraclass
correlation. For r = 2, the sample size requirement is largest for an
intraclass correlation of zero. But for r = 3, 4, 5, 10, 20, and 40 an
intraclass correlation planning value of about .26, .33, .38, .43, .44,
and .45, respectively, maximizes the sample size requirement.