When have presidential campaigns decided election outcomes?

How often and when have fall presidential general election campaigns during the past 50 years been decisive in determining which presidential candidate would receive the plurality of the national popular vote? This article addresses these questions using data from the Gallup Poll, the National Election Studies, and actual election returns for the 14 presidential elections from 1948 to 2000. Based on an analysis of four measures of net effects of general election campaigns from after the national party conventions until election day, there is some evidence of campaigns being decisive in 5 of the 14 elections examined. Campaigns after the conventions were probably decisive in two elections, the 1948 and 1960 contests, and possibly made the difference in the outcomes of the 1976, 1980, and 2000 elections. A conservative estimate is that campaigns conducted after the conventions have probably been decisive in about a quarter of presidential elections since 1948.