Polling systems across the world and how they work

FIRST PAST THE POST

Constituency-based elections; winner is the candidate who gets the most votes

Pros: Gives a clear outcome, clear link between voter and elected representative

Cons: Every vote for the loser is wasted

Used: UK, US, India, Malaysia

SINGLE TRANSFERABLE VOTE

Multi-member constituency-based elections, where voters rank their candidate preferences with each preference counted and more than one candidate elected

Pros: Seen as the "purest" proportional representation system, ensuring that all votes count for something

Cons: Incredibly complicated to work out, and breaks the clear constituent-representative link

USED: Ireland, Scotland (in local government elections since 2007)

ALTERNATIVE VOTE

Similar to First Past The Post (FPTP), but here candidates need 50 per cent of the vote to get elected. If no-one gets this, the most unpopular candidate drops out, and their second preference votes are added on to those still in, until someone gets more than 50 per cent.

Pros: Retains constituency link, ends elections where MPs win with figures as low as 30 per cent of the vote, and eliminates the need for tactical voting

Cons: Critics say it isn't representative enough, and can sometimes be even worse than FPTP, locking in the dominance of the big parties

Used: Australia, Irish presidential elections, Fiji

ADDITIONAL MEMBER SYSTEM

A hybrid between FPTP and proportional representation. Members elected in a straight constituency fight are "topped-up" with others who win through a proportional representation system designed to compensate for the FPTP imbalances.

Pros: Best of both worlds, with constituency link still maintained, but a more proportional make-up in parliament

Cons: Creates a two-tier parliament of constituency and proportional representation members, and can lead to confusion among voters

Used: Scottish Parliament