The Swiss Confederation is a federal republic with a population of 8 million. It is a consensus driven society, and its political system is characterised by decentralisation and direct democracy. There is strong pressure on federal departments, including those engaged in development policy, to justify policy choices to citizens. Referendums are mandatory for amendments to the federal constitution and for joining international organisations, for example. Referendums can also be called by citizens wishing to challenge laws passed by parliament if they gather 50 000 signatures within 100 days. Swiss NGOs successfully used the petition system with their 2007 campaign for Switzerland to adopt the target of spending 0.7% of gross national income (GNI) on official development assistance (ODA): over 200 000 people signed the petition and in 2011 a majority in parliament approved a target ODA/GNI ratio of 0.5% by 2015.