Less than 5% of the world's population lives in a "full democracy," according to a new report ranking countries by how functional their political systems are.

The Economist Intelligence Unit released on Wednesday its 2017 Democracy Index, which ranks 167 countries on a 0 to 10 scale. Only countries with scores above 8 are categorised as "full" democracies.

The US was downgraded from a "full democracy" to a "flawed democracy" in the same study last year, which cited the "low esteem in which US voters hold their government, elected representatives, and political parties."

The study has five criteria: Whether elections are free and fair ("electoral process and pluralism"), governments have checks and balances ("functioning of government"), and whether citizens are included in politics ("political participation"), support their government ("political culture"), and enjoy freedom of expression ("civil liberties").

Scroll down to see the world's best democracies.