Third, there are models that describe relationships between different variables measured at a givens point in time for different units (for example households or firms). Most of the time, this type of relationship is meant to explain why these units are different or behave differently. For example, one can analyse to what extent differences in household savings can be attributed to differences in household income. Under particular conditions, these cross-sectional relationships can be used to analyse 'what if'questions. For example, how much more would a given household, or the average household, save if income would increase by 1%