Considering high performance in PISA, a case study of Estonia and Singapore is required. Estonia's economy is not up to par with Singapore. On the other hand, Estonia is more democratic than Singapore. The national IQ levels are higher in Singapore (102) than in Estonia (99.4) but may explain a large portion of the attainment level in both countries. Singapore does also have more highly educated and better paid teachers, as well as a highly skilled foreign workforce. Annual educational quantity is very similar. Therefore, the high scores in Estonia relative to the OECD average and many wealthier western nations remain as somewhat of a minor mystery.