A map of swing-state campaigning

IT IS difficult to gauge the effectiveness of advertising and campaign visits during a presidential campaign. Vast sums have been spent on TV ads, mostly cancelling each other out. Borrell Associates, a research firm, expects some $7.4 billion to be spent on television and radio advertising tied to all this year’s elections. On current showings, there will be almost 50% more ads than in 2008 in the presidential race alone, according to the Wesleyan Media Project, an academic monitoring group. The overwhelming majority of the ads are negative. As the map shows, Mitt Romney and his allies have outspent Barack Obama and friends in most of the key states. Mr Romney has also held more events in them. If the Republican nominee becomes America's 45th president, some will argue that this edge won him the race. If he does not, it will still be possible to argue that he would have fared worse had his campaign not bought so many spots. The effectiveness of political ads remains difficult to measure, making it likely that the huge amount of money spent on them will be exceeded next time around.