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"original_study": {
"claim": {
"hypothesis": "As the number of parties in a party system increases, the dispersion of parties along the economic policy dimension increases.",
"hypothesis_location": "Introduction and Predictions of Spatial Theory sections (pages 1–4).",
"statement": "The empirical analysis shows that systems with more parties exhibit greater dispersion: in regressions of economic-policy dispersion on the number of parties, the log count of parties has a positive and statistically significant association with the log distance between the most extreme parties along the economic dimension.",
"statement_location": "Results of Empirical Analysis and Regression Analysis sections, pages 13–17, and Table 4, where the coefficient on the log count of parties predicting log economic dispersion is reported as 0.39 with a robust standard error of 0.14 and marked as statistically significant within a 95% confidence interval.",
"study_type": "Observational"
},
"data": {
"source": "Comparative Manifesto Project (CMP) data on party manifestos for parliamentary parties, combined with information on parliamentary seat shares and electoral systems in twenty established parliamentary democracies.",
"wave_or_subset": "All national parliamentary elections from the first election after the Second World War through the last election in the 1990s for twenty parliamentary democracies (Australia, Austria, Belgium, Canada, Denmark, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, New Zealand, Portugal, Spain, Sweden, Switzerland, United Kingdom).",
"sample_size": "295 country–election–year party systems (Table 1).",
"unit_of_analysis": "Party system in a given country and election year (country–election–year).",
"access_details": "not stated",
"notes": "The number of parties in a party system is measured in two ways: (1) a count of parliamentary parties that win at least 1% of seats in at least two consecutive elections (with parties dropped if they fall below 1% for three consecutive elections), and (2) the effective number of parties in parliament based on the Laakso–Taagepera formula. Party positions are estimated from CMP manifesto categories via principal components analysis to construct an economic and a social policy dimension. Party dispersion is measured as the distance between the two most extreme parties on each dimension within each party system."
},
"method": {
"description": "The authors pool party-position data from twenty parliamentary democracies over time, estimate parties’ locations on economic and social policy dimensions using CMP manifesto data, compute dispersion as the distance between the most extreme parties in each system, and regress dispersion on the number of parties (and electoral rules) to test whether systems with more parties are more dispersed.",
"steps": [
"Use Comparative Manifesto Project data to code party policy positions for parliamentary parties in twenty established parliamentary democracies from 1945 to 1999.",
"Construct two policy dimensions (economic and social) by performing principal components analysis on selected CMP issue categories, obtaining a score on each dimension for every party in every election year.",
"Define membership in the party system using a 1% parliamentary seat-share threshold over at least two consecutive elections, dropping parties that fall below 1% for three consecutive elections; for each country–election–year, count how many parties belong to the system.",
"For each country–election–year, identify the two most extreme parties along the economic policy dimension and compute the distance between them to obtain a measure of economic dispersion (and similarly for social dispersion).",
"Assemble a dataset of 295 party systems (country–election–years) including dispersion measures, the count of parties, the effective number of parties, and an indicator for single-member-district versus proportional electoral rules.",
"Log-transform dispersion and the number-of-parties measures, and estimate ordinary least squares regressions of logged dispersion on logged number of parties, electoral-system dummy, and the lagged dependent variable, clustering robust standard errors by country.",
"Interpret the coefficient on the logged count of parties as the elasticity of party dispersion with respect to the number of parties in the system."
],
"models": "Ordinary least squares regression models of the natural log of party dispersion on the natural log of the number of parties in the party system and electoral rules, including a lagged dependent variable and robust standard errors clustered by country.",
"outcome_variable": "Natural log of the distance between the two most extreme parties along the economic policy dimension in each country–election–year party system.",
"independent_variables": "Natural log of the count of parties in the party system (based on parliamentary parties with at least 1% of seats in at least two consecutive elections).",
"control_variables": "Indicator for single-member-district electoral systems versus proportional representation; lagged value of logged economic dispersion.",
"tools_software": "not stated"
},
"results": {
"summary": "Both descriptive comparisons and regression models show that party systems with more parties are more dispersed in policy space: mean distances between extreme parties increase as the number of parties rises up to about five parties, and in regression models the log count of parties has a positive and statistically significant effect on the log distance between the most extreme parties along the economic policy dimension, while electoral rules have no independent effect once the number of parties is controlled for.",
"numerical_results": [
{
"outcome_name": "Logged economic-policy dispersion (distance between most extreme parties) as a function of logged number of parties in the system",
"value": 0.39,
"unit": "OLS elasticity coefficient (percent change in economic-policy dispersion associated with a 1 percent increase in the count of parties)",
"effect_size": "OLS regression coefficient = 0.39 (Model 1a)",
"confidence_interval": {
"lower": "not stated",
"upper": "not stated",
"level": 95
},
"p_value": "< 0.05",
"statistical_significance": 1,
"direction": "positive"
}
]
},
"metadata": {
"original_paper_id": "10.1017/S0007123409990172",
"original_paper_title": "The Spatial Structure of Party Competition: Party Dispersion within a Finite Policy Space",
"original_paper_code": "not stated",
"original_paper_data": "not stated"
}
}
} |