Context: Through Congress and Inter-Congress meetings, and ongoing scientific Working Groups, PSA provides an interdisciplinary platform for scientists to discuss and review common concerns and priorities in the region. Through our scientific network, PSA links scientists from developed countries with those from developing countries, including the archipelagic and more remote states of the Pacific. PSA facilitates research initiatives on critical emerging issues for the region, such as biodiversity loss, climate change, infectious diseases, and the social implications of globalization, in which science can provide crucial information in a way that is required by both society and policymakers to make sound and informed decisions. PSA is a Scientific Associate of the International Council for Science . PSA's ongoing activities include: Multi-symposia Pacific Science Congresses, held in a different location every four years. Somewhat smaller and more topically focused Inter-Congress meetings are also held in between each Congress. The 21st Congress was held in Okinawa, Japan in June 2007, and the 11th Inter-Congress was held in Tahiti, French Polynesia in March 2009. The next Congress will be at the Kuala Lumpur Convention Center in Kuala Lumpur, Malaysia from 13-17 June 2011. Pacific Science, the official journal of the PSA. Pacific Science is a quarterly journal devoted to the biological, physical, and social sciences of the Pacific Region.

Question: How many years between the 21st Congress and the 11th Inter-Congress?

Answer:
2