What are the observed ranges of values that define tercile groups?
For each indicator countries are divided into three groups of approximately equal size (terciles) according to the observed value—the top third, the middle third and the bottom third. Sex ratio at birth is an exception—countries are divided into two groups: the natural group (countries with a value between 1.04–1.07, inclusive) and the gender-biased group (all other countries). Deviations from the natural sex ratio at birth have implications for population replacement levels, which suggest possible future social and economic problems and may indicate gender bias. Countries with values of a parity index concentrated around 1 form the group with the best achievements in that indicator. Deviations from parity are treated equally regardless of which gender is overachieving. The intention is not to suggest thresholds or target values for these indicators. See Technical note 6 at http://hdr.undp.org/sites/default/files/hdr2016_technical_notes.pdf for details about observed ranges of values and the number of countries in “tercile” groups for indicators in Life-course gender gaps dashboard.