“…It is simply the function that summarizes the relationship between individual preferences and household choices. In the general formulation of the collective model (Cherchye et al, 2015), the weight λ may depend on a variety of factors including outside options for the partners, wage rates, total expenditure and prices.If λ is fixed, then the collective model is equivalent to a unitary model of the household (Vermeulen, 2002). So the collective model can be seen as a generalization of the unitary model that allows λ to vary with the environment faced by the household.Cooperative models such as McElroy and Horney (1981) and Manser and Brown (1980) represent a third approach in which further structure is placed on λ, usually by being specific about fall-back options and adding axioms about the solution to the household bargaining problem, the most common of which is the Nash bargaining solution.…”