In a book about the "why" of these institutions, John Aldrich argued that they are highly endogenous.
Giovanni Sartori's book on these institutions characterizes them "as part" and "as whole." In a book about the "why" of these institutions, John Aldrich argued that they are highly endogenous. According to the Lipset-Rokkan hypothesis, these institutions have been divided by four cleavages that emerged in the 1920s. Richard Katz and Peter Mair have claimed that, since the 1970s, the "cartel" type of these institutions has arisen. Markku Laakso and Rein Taagepera proposed using the inverse Simpson's index to calculate the effective number of these institutions, which name a book that distinguishes their "elite- based" and "mass-based" types. They also name the book in which Robert Michels stated his "iron law of oligarchy." According to Duverger's Law, plurality rule and proportional representation tend to favor systems with two of them. For 10 points, name these political organizations that seek to achieve common goals, which include the Republicans and the Democrats.
Giovanni Sartori's book on these institutions characterizes them "as part" and "as whole.
1.	political parties [accept word forms or party systems or Parties and Party Systems or Why Parties]