Beginning in the 1990s, a separate approach to quantum social science was taken by a number of interdisciplinary researchers, working in what became known as quantum cognition, who argued that quantum probability theory was better than classical probability theory at accounting for a range of cognitive effects of the sort studied in behavioral economics. Others worked on developing "weak" or "generalised" versions of quantum theory which extended concepts such as complementarity and entanglement to the social domain. In their 2013 book Quantum Social Science, Emmanuel Haven and Andrei Khrennikov developed mathematical formalisms for the application of quantum models to topics including psychology, economics, finance, and brain science.