What is the advantage of grouping countries into five GDI groups instead of ranking them according to the absolute deviation from parity?

Estimating the female and male HDIs for all countries relies on many approximations, such as assuming wage ratios of 0.8 for many countries. Because of this the estimated HDIs need to be interpreted with caution. We prefer not to rank the countries based on these approximated HDIs. Instead, we group countries into five GDI groups by absolute deviation from gender parity in HDI values.

Group 1 countries have high equality in HDI achievements between women and men: absolute deviation less than 2.5 percent; group 2 has medium-high equality in HDI achievements between women and men: absolute deviation between 2.5 percent and 5 percent; group 3 has medium equality in HDI achievements between women and men: absolute deviation between 5 percent and 7.5 percent; group 4 has medium-low equality in HDI achievements between women and men: absolute deviation between 7.5 percent and 10 percent; and group 5 countries has low equality in HDI achievements between women and men: absolute deviation from gender parity greater than 10 percent.