Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I even say who wrote them. If you have more recent summaries to add to this collection, send them my way I guess. Sorry for the ads; they cover the costs of keeping this online.
Lau, Sigelman, Heldman, and Babbitt. 1999. The effects of negative political advertisements. APSR 93:851-75.
Many studies of negative advertising have been done. They tend to address three questions: (1) whether negative ads "work," (2) whether people dislike them, and (3) whether negative ads lead to a disengagement with politics. Yet these studies are not cumulative. Thus, this paper performs a meta-analysis in an effort to aggregate the findings of dozens of studies to determine whether, on the whole, negative ads seem to matter.
No, negative ads don't matter. Although some studies find significant effects, these are balanced out by studies that do not. The authors control for a variety of factors that differentiate these studies: experiment vs survey, large- vs small-sample, actual vs fake ads, more recent vs older studies, subjectively "good" vs "bad" studies, etc. Even controlling for these factors, the literature does not produce a consistent result that negative ads have significant effects.
See the article. In brief, meta-analysis works like this:
Research by the same authors
Research on similar subjects