Measures such as employment equity were implemented in developed nations in the 1970s to 1990s, but these were not entirely successful in removing wage gaps even in nations with strong equity traditions. Systemic study of the ways that women's work is undervalued, undertaken by Marilyn Waring and others in the 1980s and 1990s, began to justify different means of measurement of value - some of which were influential in the theory of social capital and individual capital, which emerged in the late 1990s and ultimately merged with ecological economics to become modern human development theory.
Jane Jacobs' thesis of the "Guardian Ethic" and its contrast to the "Trader Ethic" was also influential in explaining in ethical terms why a trading culture would systematically undervalue guardianship activity, including the child-protecting, nurturing, and healing tasks that were traditionally assigned to women. This led to the more general idea of systems as expressing either tolerances or preferences, and never being very good at both.
Critics of the theses of Waring, Jacobs, and other feminists who explore the role of women in the economy, argue that protective activities, e.g. military and police and government, are just as much male as female roles, more so in times of chaos, and that these proceeding theories are sexist.