The total length of the bars indicates the observed variation in the index of familiarity with mathematics. The variation in familiarity with mathematics is more than four times greater in Liechtenstein and Spain than in Indonesia. Across OECD countries, around 86% of the country-level variation in familiarity with mathematics can be traced to differences across students who attend the same school, while around 14% can be ascribed to differences across students who attend different schools.