The latest version of the Polity Project, the Polity IV, is a continuation of a research programme established by Ted Robert Gurr in the 1970s. Originally, the aim of the project was to measure political system durability. In subsequent years, the analytical scope was broadened to encompass the issue of regime type more generally, and today the project’s main index is a measure of the degree of democracy and autocracy (Jaggers and Gurr 1995: 470).
The project is currently under the direction of Monty G. Marshall at the Center for Systemic Peace and George Mason University.
Polity IV dataset
Data types and sources
Ordinal-scale indicators. Expert coding based on a subjective interpretation of historical monographs and other source materials.
The Polity scheme consists of six component measures that record key qualities of executive recruitment, constraints on executive authority, and political competition. The most widely used of the indices is the Polity score, which combines the scores on the democracy and autocracy indices to a single regime indicator. The score captures the regime authority spectrum on a 21-point scale ranging from -10 (hereditary monarchy) to +10 (consolidated democracy). The component variables that are used to construct the composite indices are also published in disaggregate form.
The dataset covers all independent states with a total population greater than 500.000.
Time coverage and updates
Years covered: 1800-2010.Long-established countries are coded beginning in 1800; more recently established countries are coded from the year in which their first independent government was formed. The dataset is updated and revised on an annual cycle and, according to the project homepage, be reexamined whenever new sources of information becomes available. The Appendix A of the Polity IV Project: Dataset Users’ Manual provides an overview of each country’s time series coverage.
The dataset is described in detail in Polity IV Project: Dataset Users’ Manual (Marshall, Jaggers and Gurr 2011). The users’ manual gives a brief introduction to the background of the Polity Project, developments and improvements made to the dataset since its first version and also specifies the coding rules for each variable. An earlier version of the dataset is described in Jaggers and Gurr (1995).
Access conditions and cost
Available free of charge.
Predefined table. The entire dataset can be downloaded in a single file, organised in country-year format.
The annual time-series and the polity-case datasets are available in SPSS and Excel format.
Comparability and data quality
All attempts to measure a concept such as democracy – and all indicators that are based on subjective interpretations – are bound to be uncertain and contested. So also with the Polity Project, which is sometimes criticised for relying on a too minimalist definition of democracy and for not offering a theoretical justification for the way the component variables are aggregated to a single regime index. On the other hand, the Polity indices are among the most widely used indices of democracy and is often given credit in terms of the reliability of the index: the coding rules are clearly specified in the users’ manual, the component variables are presented in disaggregate form and several coders are used in the coding process.
See Hadenius and Teorell (2005), Munck and Verkuilen (2002) and Chapter 5 in Rydland et al. (2008) for a detailed discussion of the comparability and quality of democracy indices in general. For independent reviews of the Polity index in particular, see Gleditsch and Ward (1997) and Goertz (2006: chap. 4).
Beetham, David (ed.). 1995. Defining and Measuring Democracy. Thousand Oaks: Sage.
Bogaards, Matthiijs. 2007. “Measuring Democracy through Election Outcomes: A Critique with African Data”. Comparative Political Studies (40) 10: 1211-1237.
Bollen, Kenneth A. and Pamela Paxton. 2000. “Subjective Measures of Liberal Democracy”. Comparative Political Studies (33) 1: 58-86.
Casper, Gretchen and Claudiu Tufis. 2003. “Correlation versus Interchangeability: The Limited Robustness of Empirical Findings on Democracy Using Highly Correlated Datasets”. Political Analysis 11 (2): 196:203.
Collier, David and Robert Adcock. 1999. “Democracy and Dichotomies: A Pragmatic Approach to Choices about Concepts”. Annual Review of Political Science 2: 537-565.
Elkins, Zachary. 2000. “Gradations of Democracy? Empirical Tests of alternative Conceptualizations”. American Journal of Political Science 44 (2): 287-294.
Gerring, John. 2008. “Measuring Democracy: Proposal for a Disintegrated Approach”. 104th Annual Meeting , American Political Science Association (APSA), Boston, Massachusetts, 28-31 August.
Gleditsch, Kristian S., and Michael D. Ward. 1997. “Double take: a reexamination of democracy and autocracy in modern polities”. Journal of Conflict Resolution 41 (June): 361-383.
Goertz, Gary. 2006. Social Science Concepts: A User’s Guide. Princeton and Oxford: Princeton University Press.
Jaggers, Keith, and Tedd Robert Gurr. 1995. “Tracking democracy’s third wave with the Polity III data”. Journal of Peace Research 32 (November): 469-482.
Munck, Gerardo L., and Jay Verkuilen. 2002. “Conceptualizing and measuring democracy: evaluating alternative indices”. Comparative Political Studies 35 (February): 5-34.
Rydland, Lars Tore, Sveinung Arnesen and Åse Gilje Østensen. 2008. Contextual data for the European Social Survey. An Overview and assessment of extant resources. NSD Report No.124, Norwegian Social Science Data Services (NSD).