From CBC News:
Mitt Romney's choice of Paul Ryan as his running mate seems to have produced a rare bipartisan moment of glee for Republicans and Democrats as both seem overjoyed by the decision. The impact Ryan will have on Romney's candidacy remains to be seen. Many believe the vice-presidential pick has little impact on the political fortunes of the presidential candidate. A study by political scientists at the University of California, Irvine, that evaluated the impact of vice-presidential selection on voter choice, backs that view. It found that the net impact of vice-presidential selection is at most one percentage point in total votes. And in 2008, when John McCain chose Palin as his running mate, the impact was only about one-half of a percentage - slightly lower than the historical average.

For the full story, please visit http://www.cbc.ca/news/world/story/2012/08/13/romney-ryan-running-mate.html.