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Introduction

JUDGEIT II brings the analytical routines of the original version of JUDGEIT to the R Project for Statistical Computing, while also greatly simplifying its interface and control system.⁴ The methods implemented in this software were developed in Gelman, Katz & King (2004); (); King & Gelman (1991); Gelman & King (1990b,a,1994).

JUDGEIT allows a user to construct a model of a two-party election system over multiple election cycles, derive quantities of interest about the system through statistical estimation and simulation, and produce output summary statistics and graphical plots of those quantities. Some of the quantities of interest are based on partisan symmetry as a standard of fairness in legislative redistricting, such as partisan bias as the deviation from fairness and electoral responsiveness which indexes how party control of legislative seats responds to changes in a party's success at the polls even in a fair system. (A uniform consensus has existed in the academic literature since at least King & Browning (1987) on partisan symmetry as a standard for fairness, and even the U.S. Supreme Court now appears to agree; see Grofman & King 2007.) JUDGEIT also estimates and graphs seats-votes curves, make specific vote and seat predictions for individual districts, and calculate numerous other relevant statistics.

The program can evaluate electoral systems in three general situations:

1. When an election already has taken place,
2. When an election has not been held yet but a new redistricting plan (or plans) has been proposed or implemented, and
3. When you wish to assess what an election would have been like if held under certain specified counterfactual conditions (such as if no minority districts had been drawn, or term limitations had prevented incumbents from running for reelection).

For bias, responsiveness, seats-votes curves, and virtually every other estimate, JUDGEIT provides quantitative estimates of uncertainty (i.e., standard errors or confidence intervals). This are recognized as essential by social scientists and even the Supreme Court (see Castaneda v. Partida, 430 U.S. 482, 1977, and Hazelwood School District v. United States, 433 U.S. 299, 1977).