Previous studies of the impact of campaign spending on US House elections have reported that while expenditure by challengers seems to influence the vote, expenditure by incumbents is ineffective. It is argued that these results are spurious, and that instead it is the ratio of challenger expenditure to incumbent expenditure that is important. This means that both challenger spending and incumbent spending matter via their roles in constituting this ratio. Analysis of data from the 1988 US House election supports this hypothesis.