What is one criterion used by parties to determine the number of delegates sent to each state?

The correct answer focuses on party loyalty, which is a significant criterion for determining the number of delegates a state sends to a national convention. Political parties aim to reward and mobilize their most loyal supporters when allocating delegates, as these individuals are often more likely to engage with the party, vote in elections, and participate in party activities. By reflecting party loyalty in the delegate allocation process, parties can ensure that they are representing those who are most invested in their political platform and goals.

Other factors like a state's geographical location, age of voters, and voting history can influence political dynamics and strategic considerations, but they do not directly dictate the number of delegates allocated to a state. Geographical location could affect campaigning strategies or voter demographics, age of voters might inform policy priorities, and voting history can indicate trends in electoral support, yet these factors do not play a formal role in delegate distribution within party rules.