The sleeper effect and negative political advertising

The sleeper effect phenomenon is examined to explain how the impact of negative political advertising persists -and even increases -over time. Using a true experimental design with attack and defensive message treatments, adult subjects were asked to report their vote and its certainty immediately after message exposure and in a delayed telephone callback. Results indicate that a defensive advertisement following the attack is initially effective; however, over the next few weeks, the impact of the attack ad increases substantially. Similarly, an initial perception that the assailant has low credibility has only a temporary suppressive impact on the effectiveness of the attack ad. Our documentation of both an order-driven and a credibility-driven sleeper effect poses strategic challenges for those candidates who are attacked. Further, these results offer theoretical insights into the determinants and the pervasiveness of the sleeper effect in political campaigns.