Given the prevailing two-party system in the United States, presidential primary and caucus outcomes strongly influence the choices available to voters in presidential elections. While the Democratic Party has strong national rules on how delegates are to be awarded from primaries and caucuses, the Republican Party allows significant local discretion in crafting rules that translate primary and/or caucus outcomes into pledged delegates. This is significant because delegate vote totals determine who becomes the party's nominee. Little is known, though, about the rationale for selecting different rules for delegate allocation. We develop a method for classifying delegate allocation rules using a three-category scale as winner take all, fully proportional, or mixed. We then evaluate how different factors, including state ideology, state size, and the number of states holding a primary on the same day can influence rules by which election results are translated into delegate counts.