Proportion of third-level variation in multi-level studies: A note on an interval estimation procedure.

An interval estimation procedure is outlined that can be used for evaluating the proportion of observed variance in a response variable, which is due to the third level of nesting in a hierarchical design. The approach is also useful when it is of concern to address the necessity of including a third level in analyses of data from a multi-level study, relative to an alternative of proceeding with two-level modelling. The proposed method is illustrated with an empirical example.