A national party convention is a meeting held by a political party for the purposes of nominating a presidential and vice presidential candidate and adopting a party platform. These conventions occur once every four years, during the presidential election season, and are now normally four days long. Over the years, this convention has become more of a public party advertisement than a governing, decision-making entity. This shift can be clearly seen by observing two modern traits of national party conventions. First, the selection of presidential and vice presidential candidates is now decided more by voters and party-wide elections than private caucuses. Second, these events are now heavily scripted functions, for much of the convention is aired on television.