Do two parties represent the US? Clustering analysis of US public ideology survey

Recent surveys have shown that an increasing portion of the US public believes the two major US parties inadequately represent the US public opinion, and think additional parties are needed [1]. However, there are high barriers for third parties in political elections. In this paper, we aim to address two questions: “How well do the two major US parties represent the public’s ideology?” and “Does a more-than-twoparty system better represent the ideology of the public?”. To address these questions, we utilize the American National Election Studies Time series dataset [2], a dataset of opinion surveys of 20,502 individuals over multiple political issues since 1948. We perform unsupervised clustering with Gaussian Mixture Model method on this dataset, and we find the cluster center found under a two-cluster restriction is close to the party centers, which are estimated using the mean position of the individuals self-identified with the parties. We conclude that the major US parties are representative of the US population under the constraint that the political system is limited to two parties. We investigate if more than 2 parties represent the population better by comparing the Akaike Information Criteria for clustering results of various number of clusters. We find that additional clusters give better representation of the data, even after penalizing for the additional parameters. This suggests a multiparty system represents of the ideology of the public better.