Parliamentary structure in member states varies: there are 15 unicameral national parliaments and 12 bicameral parliaments. The prime minister and government are usually directly accountable to the directly elected lower house and require its support to stay in office—the exceptions being Cyprus and France with their presidential systems. Upper houses are composed differently in different member states: it can be directly elected like the Polish senate; indirectly elected, for example, by regional legislatures like the Federal Council of Austria; or unelected, but representing certain interest groups like the National Council of Slovenia. All elections in member states use some form of proportional representation. The most common type of proportional representation is the party-list system.