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Biographical Fields:

• congress: Integer 1+. The number of the congress that this member's row refers to. e.g. 115 for the 115th Congress (2017-2019)
• chamber: House, Senate, or President. The chamber in which the member served.
• icpsr: Integer 1-99999. This is an ID code which identifies the member in question. In general, each member receives a single ICPSR identifier applicable to their entire career. A small number of members have received more than one: this can occur for members who have switched parties; as well as members who subsequently become president. Creating a new identifier allows a new NOMINATE estimate to be produced for separate appearances of a member in different roles.
• state_icpsr: Integer 0-99. Identifier for the state represented by the member.
• district_code: Integer 0-99. Identifier for the district that the member represents within their state (e.g. 3 for the Alabama 3rd Congressional District). Senate members are given district_code 0. Members who represent historical "at-large" districts are assigned 99, 98, or 1 in various circumstances.
• state_abbrev: String. Two-character postal abbreviation for state (e.g. MO for Missouri).
• party_code: Integer 1-9999. Identifying code for the member's party. Please see documentation for Party Data for more information about which party_code identifiers refer to which parties.
• occupancy: Integer 1+. ICPSR occupancy code. This item is considered legacy or incomplete information and has not been verified. In general, members receive 0 if they are the only occupant, 1 if they are the first occupant, 2 if they are the second occupant, etc.
• last_means: Integer 1-5. ICPSR Attain-Office Code. This is an indicator that reflects the member's last means of attaining office. This item is considered legacy or incomplete information and has not been verified. Members received 1 if they were elected in a general election, 2 if elected by special election, 3 if directly elected by a state legislature, and 5 if appointed.
• bioname: String. Name of the member, surname first. For most members, agrees with the Biographical Directory of Congress.
• bioguide_id: String. Member identifier in the Biographical Directory of Congress.
• born: Integer. Year of member's birth.
• died: Integer. Year of member's death.

Ideological Fields:

• nominate_dim1: NOMINATE first dimension estimate.
• nominate_dim2: NOMINATE second dimension estimate.
• log_likelihood: Log-likelihood of the NOMINATE estimate.
• geo_mean_probability: Geometric mean probability of NOMINATE estimate.
• number_of_votes: Number of votes cast by the member during a given congress.
• conditional: Integer 0-1. A 1 indicates NOMINATE was estimated conditionally for a given member. 0 otherwise. Conditional estimation implies that an estimate is provisional and subject to updates when the next full estimation of NOMINATE scores occurs.
• nokken_poole_dim1: Nokken-Poole First dimension estimate.
• nokken_poole_dim2: Nokken-Poole Second dimension estimate.

Making use of Ideological Data

We present two main estimates of a legislator's ideology: NOMINATE and Nokken-Poole. NOMINATE estimates assume that members occupy a static ideological position across the course of their career. Nokken-Poole estimates assume that each congress is completely separate for the purposes of estimating a member's ideology. We expect that most users of our data will primarily make use of the nominate_dim1 field, which reports the first dimension (often interpreted as economic liberalism-conservatism) of members as estimated by NOMINATE.

For more information on these scores, please see discussion in our journal article:

Boche, Adam, Jeffrey B. Lewis, Aaron Rudkin, and Luke Sonnet. "The new Voteview.com: preserving and continuing Keith Poole’s infrastructure for scholars, students and observers of Congress". Public Choice 176(1-2). Available online: https://link.springer.com/article/10.1007/s11127-018-0546-0