For more details on the Referendum Database, please refer to the RDB codebook (Brüggemann 2023).

Ballot date

Date on which at least one referendum was held in a country. In our analysis, we oftentimes look at ballot dates instead of referendums. This is because in the Referendum Database, for example a popular vote on a new constitution, each article of this constitution is counted as an individual referendum.

In general, differentiating between referendums and ballot dates entails a few tradeoffs:

  • If we look at single referendums, the danger is that we count different response options to the same question as distinct events.

  • If we only look at unique ballot dates per country, we solve this problem. However, we also lose distinct referendums that took place on the same date.

  • Ideally, we would include an additional variable in the Referendum Database denoting if referendums taking place on the same date belong together or if they are distinct.


In this report, we treat as “countries” those territorial units that hold referendums independently. Excluded from this are sub-national entities, such as federal states in the USA or cantons in Switzerland. Territories differ from federal states in that they may have a certain degree of autonomy, but they do not have the same extensive rights as federal states or provinces. As an example serves Greenland, which belongs to Denmark. Although Greenland is not a province in its own right, it has far-reaching rights of self-determination. For example, the Greenlandic population can also decide on their own independence by referendum.

We rely on the classification into territorial units, based on the ISO standard ISO 3166 that includes independent countries, territories and regions of geographical interest. Furthermore, ISO 3166-3 is used for historical countries that no longer exist.

Legal basis

Several authors have identified the legal basis as an important aspect of referendums (Suksi 1993; Gallagher 1996; Setälä 1999; Altman 2017). In the RDB, legal basis can take on the following values:

  • non-official: The referendum type has no legal basis.
  • ad-hoc: The referendum type has a legal basis which was specifically created for it.
  • official: The referendum type has a legal basis that wasn’t specifically created for it.
Referendum instances

In the RDB, we use the term referendum to refer to “[…] any popular vote on an issue of policy that is organized by the state or at least by a state-like entity, such as the authorities of a de facto state” (Mendez and Germann 2016, 144).

Regime type

For regime type, we refer to the Regimes of the World (RoW) classification developed by the Varieties of Democracy (V-Dem) project (Coppedge et al. 2023). This classification divides countries into the following four types, according to the competitiveness of access to power (polyarchy) and liberal principles:

  • closed autocracy
  • electoral autocracy
  • electoral democracy
  • liberal democracy

Additionally, we also use data compiled by Freedom House (2023) for robustness checks.


Share of registered voters participating in a referendum.


The way the referendum is triggered:

  • automatic: The referendum is triggered by a constitutional/legal requirement.
  • top down: The referendum is triggered by an institution of the political elite like the monarch/president/government, the parliament, a territorial unit, the UN or another institution.
  • bottom up: The referendum is triggered by citizen demand (e.g. a signature collection).
Waves of democratization

For the World of Referendums Report 2023, we aim to show how many and which type of referendums have occurred over different time periods. For these time periods, we refer to the original work done by Huntington (1993) and refined by Lührmann and Lindberg (2019).

World region

To categorize countries into world regions, we rely on the United Nations (UN) geoscheme which subdivides all countries into up to three different grouping tiers based on the UN M49 area code hierarchy.

See the documentation of the R function rdb::add_world_regions() for further details.