This package is no longer maintained. I recommend using the dwnominate package for R instead of this gem. It should be more convenient in most cases.

nominate

The 'nominate' gem, to run W- and DW-NOMINATE from Ruby

W-NOMINATE uses rollcall votes to map legislators along a political spectrum. In American state and federal elections, it typically finds the traditional left-right spectrum. DW-NOMINATE uses legislators who have served in multiple legislative sessions to compare sessions and track changes through time.

Installation: sudo gem install nominate

Requirements

• Linux
• R
  In Ubuntu: sudo apt-get install r-base r-base-dev
• GFortran (only for DW-NOMINATE)
  In Ubuntu: sudo apt-get install gfortran

Example

Let's say you have a file of voting data in the format

name1|party1|rollcall1 info|vote1
name2|party2|rollcall1 info|vote2
...
name1|party1|rollcall2 info|vote1
name2|party2|rollcall2 info|vote2
...

which is similar to what you can download from the New Hampshire state legislature. And these are collected in file '1999NHrollcalls.csv' and so forth.

The following code will read the rollcall data into Wnominate objects, and add the sessions to a Dwnominate object. chamber.dwnominate starts the nominate process, first calling wnominate on each Wnominate object, then using the results to write the input files for the DW-NOMINATE program, and then running DW-NOMINATE. All results, including output graphs from the R wnominate package, will be written to a folder called 'nominate'.

An alternative is to call wnominate(prefix) on Wnominate objects, which will run only the W-NOMINATE program, adding the specified prefix to each output file.

require 'nominate'

chamber = Dwnominate.new

# votes other than Yes or No are counted as missing ('M')
vote_key = Hash.new('M')
vote_key['Yes'] = 'Y'
vote_key['No'] = 'N'
# Wnominate object only accepts 'Y', 'N', and 'M' votes

['1999', '2001', '2003', '2005', '2007'].each do |year|
  file = year + 'NHrollcalls.csv'
  lines = IO.readlines(file)
  session = Wnominate.new
  # default party is 'unknown'
  parties = Hash.new('unknown')
  old_issue = 0
  # default vote is 'M' for 'missing'
  rollcall = Hash.new('M')
  lines.each_with_index do |line, i|
    data = line.split('|')
    name = data[0]
    party = data[1]
    issue = data[2]
    vote = vote_key[data[3].chomp]
    # every time we get to a new rollcall, add the hash with the old rollcall's votes to the
    # Wnominate object, and start a new rollcall hash.
    if issue != old_issue
      session.add_rollcall(rollcall) unless i == 0
      rollcall = Hash.new('M')
      old_issue = issue
    end
    rollcall[name] = vote
    parties[name] = party if not parties.has_key?(name)
    # get the last rollcall when you reach the end of the file
    session.add_rollcall(rollcall) if i == lines.length - 1
  end
  # add a hash of legislator names and parties if you want party info to be included
  session.parties = parties
  chamber.add_session(session)
end

chamber.dwnominate(prefix = 'dw_')

More Resources

• Scaling Roll Call Votes with W-NOMINATE in R
• R wnominate package documentation
• DW-NOMINATE at voteview.com (with an explanation of the output format)
• Spatial Models of Parliamentary Voting, by Keith Poole, an in-depth explanation of the programs
• Ideology and Congress, by Keith Poole and Howard Rosenthal