Fredrickson is a social psychologist who conducts research in emotions and positive psychology. Her main work is related to her broaden-and-build theory of positive emotions, which suggests that positive emotions lead to novel, expansive, or exploratory behavior, and that, over time, these actions lead to meaningful, long-term resources such as knowledge and social relationships. She is the author of "Positivity: Top-Notch Research Reveals the 3-to-1 Ratio That Will Change Your Life" (2009), a general-audience book that draws on her own research and that of other social scientists. The book's thesis is largely drawn from her work with Marcial Losada, claiming a mathematical ratio for happiness. The ratio, however, was, "based on a series of erroneous and, for the most part, completely illusory 'applications' of mathematics." Fredrickson was unable to reproduce the math behind her research published with Losada and has yet to disavow or apologize for the fraud. In a later response, the mathematical models for the paper were formally withdrawn.