Figure 2.

Venn diagrams for a two-facet design (person × item × occasion) are shown. Total observed score variance is shown on the top and score variance is represented by the circles. Each circle represents a facet, and the overlap between circles represents interactions between facets. Generalizability coefficients ($E{\rho }^2$) only consider variance sources in the error term that impact the relative standing or ranking of participants (i.e., relative error) in the estimation of reliability. Therefore, only variances that overlap with the ‘Person’ circle will be included in the estimation of reliability. The contribution of error variance to the generalizability coefficient of equivalence and stability (CES; see Table 1) includes only those facets that interact with person scores: the interaction between person and item (${\sigma }_{pi}^2$), the interaction between person and occasion (${\sigma }_{po}^2$), and the three-way interaction (${\sigma }_{pio,e}^2$). The contribution of error variance to the dependability ($\varphi$) CES includes all facets and interactions between facets (absolute error variance).