WASHINGTON -- Two surveys released after Thursday's vice presidential debate found both candidates made strong impressions on voters, but differed on who performed best.
A CNN survey of registered voters who watched the debate and had previously agreed to be interviewed found Paul Ryan the winner, 48 percent to 44 percent, but that was well within the survey's five percentage point margin of error. Respondents also said they thought Ryan communicated more clearly than Vice President Joe Biden, by a 50 percent to 41 percent margin, and that Ryan was more likable, 53 percent to 43 percent.
Those margins likely reflect the underlying partisan composition of the debate viewers that CNN interviewed. The cable network reported that slightly more Republicans viewed the debate (33 percent) than Democrats (31 percent), while 34 percent identified as independents.
The candidates performed similarly on whether respondents thought they were qualified to be president: 60 percent thought Ryan qualified and 38 percent did not. They said Biden was qualified by a 57 percent to 42 percent margin.
Fifty-five percent of CNN respondents said Biden performed better than they expected, 26 percent said he did worse, and 18 percent said he did the same as they expected. Ryan also impressed, with 51 percent saying he performed better, 19 percent worse, and 28 percent said he performed the same.
CNN surveyed 381 registered voters who had participated in a previous CNN poll, watched the debate, and agreed to be interviewed.
A CBS News poll of uncommitted voters using an online panel found that both candidates made solid impressions, but that more of those voters felt that the debate was a win for Biden. The survey found that 50 percent thought Biden won, 31 percent that Ryan won, and 19 percent that the debate was a tie.
Biden saw a big increase from before the debate in the percentage of respondents who thought he had the ability to be an effective president if necessary. Prior to the debate, 39 percent said he had the ability to be an effective president, while 56 percent said so after. Ryan saw a smaller increase on this measure, from 45 percent before the debate to 49 percent after.
Biden also impressed respondents with his knowledge of the issues. After the debate, 85 percent of respondents said Biden was knowledgeable on the issues, while 75 percent said so of Ryan.
The candidates were more closely matched on whether respondents said they could relate to them. Before the debate, 34 percent of respondents said they could relate to Biden, while 55 percent said so after. Ryan's rating on the measure increased from 31 percent to 48 percent.
The CBS News poll was conducted using the GfK KnowledgePanel, a representative Internet panel, to interview 431 uncommitted voters who watched the debate, and had a five percentage point margin of error. The CBS "uncommitted voters" include those who were either totally undecided before the debate or who were leaning to a candidate, but said they may still change their minds. According to CBS, 58 percent of respondents identified as independents, 17 percent as Republicans, and 25 percent as Democrats.
After last week's first presidential debate between President Barack Obama and Mitt Romney, both the CNN and CBS post-debate surveys found Romney with a big victory. Polls conducted over the course of the past week have shown a bounce for Romney in national and state polls.
Evidence from previous races suggests that even when one candidate clearly dominates in the vice presidential debate, it is unlikely to be so much of a game-changer. Although some vice presidential debates have influenced a news cycle or two, research by political scientist Thomas Holbrook has found that even the most highly publicized debates make little impact on the campaign as a whole. Likewise, historical data provided by Gallup shows that vice presidential debates make "almost no difference" in changing vote preference after the debate.
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