The Jordanian educational system comprises 2 years of pre-school education, 10 years of compulsory basic education, and two years of secondary academic or vocational education, after which the students sit for the General Certificate of Secondary Education Exam (''Tawjihi)'' exams. Scholars may attend either private or public schools. According to the UNESCO, the literacy rate in 2015 was 98.01% and is considered to be the highest in the Middle East and the Arab world, and one of the highest in the world. UNESCO ranked Jordan's educational system 18th out of 94 nations for providing gender equality in education. Jordan has the highest number of researchers in research and development per million people among all the 57 countries that are members of the Organisation of Islamic Cooperation (OIC). In Jordan there are 8060 researchers per million people, while the world average is 2532 per million. Primary education is free in Jordan.