the units of randomization, often called groups or clusters, nested within the study conditions or arms.
intraclass correlation coefficient or intracluster correlation coefficient.
the expected average correlation for the outcome among members of the same group or cluster at the time of the analysis, usually at the posttest. It is also defined as the proportion of variance in the outcome attributable to group membership at the time of the analysis, usually at the posttest.
a factor is nested if it appears within only one level of a factor higher in the hierarchy. Subjects are nested within groups or clusters if they appear in only one group or cluster. Groups are nested within study conditions if they appear in only one study condition.
randomized controlled trial, or randomized clinical trial, where the units of assignment and observation are the study participants, and where participants have no interaction with each other or with a common change agent post-randomization.
the stratification levels, e.g., high vs. low.