Sleeper Effect

The counterintuitive finding that persuasive messages from low-credibility sources become MORE persuasive over time, not less. Initially, you discount the message because the source is unreliable. Over time, you remember the content but forget the source—and the discounting fades. A rumor from an unreliable source is dismissed initially but, weeks later, you vaguely remember the claim without remembering you'd dismissed it. In marketing: ads from distrusted sources may be ineffective immediately but slowly become effective as the source-content association weakens. The sleeper effect reverses the normal pattern where persuasion decays over time.

When to use it

When old, dismissed information is resurfacing as vaguely remembered 'facts'; when misinformation from unreliable sources is gaining traction over time; when persuasion campaigns need to account for delayed effects; when designing communication strategies that anticipate source-content dissociation.

How it can help

When managing information and persuasion: be aware that source credibility fades faster than message content. Defensively: when you dismiss a claim because of its source, note the dismissal alongside the claim—otherwise the sleeper effect may cause you to accept it later. Offensively: understand that persistent messaging from even low-credibility sources can be effective over time as source associations weaken. For brand management: even unfair negative claims can become 'things people vaguely know' over time. The implication: addressing misinformation quickly matters because once the content separates from the source, it becomes harder to counter.