The subsequent step in the analysis searches for the relationship
between the different indicators. Glass (1976)
proposes meta-analysis to relate the results of different statistical
estimates for the purpose of estimating global relationship
between drawing parameters (Thompson & Sharp,
1999). This permits to determine the level of heterogeneity
of a particular group compared to the heterogeneity within
the population; the coefficient of variation captures the heterogeneity
inside a group (i.e. Higgins & Thompson, 2002;
Molinero, 2003; Raudenbush & Bryk, 1985). Equation. (1)
shows the dispersion formula