The family's relationship to the use of development assistance is modelled in different ways for different purposes. Until now, the analysis of intra-household factors has been constrained by the expense of collecting detailed and highly accurate information.

The unified preference function, according to which household members e.g. parents are assumed to allocate resources as if they have common preferences, remains useful for determining the effects of price changes on demand for basic commodities i.e. foods or nutrients. This information is essential to permit governments to use such means as tariffs, support prices, or export prices to modify the price structure in ways that protect poor families. For macro or regional policy purposes, a price subsidy to increase food consumption of a population or a segment of the population can be implemented with the assumption that households will re-allocate this food to their members. This is the least expensive approach because household-level income and consumption data are sufficient.

The household unified preference function, however, offers little information regarding to what extent changes in food prices affect individual family members; for this purpose, individual food intake or other commodity consumption is needed. Collecting individual food intake data is difficult and costly. In place of food consumption data, Rosenzweig and Behrman suggest using individual biological outcomes i.e health or nutritional status to analyse, for example, how changes in exogenous factors such as the prices of food or medical services result in changes in the health of individuals. This is called the "health reduced-form relation." If policy makers need to know the person-specific demand equations to analyse the consequences of government policy regarding the welfare of the individual, this framework can be used.