The “simplified” model has income and preference constraints, and no inheritance. The consequences of a stagnant economy defined by a lack of economic growth or population growth results in an unchanged savings rate. However, in a steadily growing economy, the national savings rate is consistent with life cycle behavior and with a higher overall savings rate in the long run. The article carefully distinguishes between the causes of increased or positive savings rates, using the Neisser and Bentzel effects, growth due to population increase, and increased productivity, respectively. Friedman found that productivity growth should decrease the saving rate because an increase in permanent income would increase consumption relative to an increase in income decreasing the saving rate. However, Modigliani found that if consumers planned without anticipating their future consumption, then wages and savings based on productivity growth would be the same. For example, in the United States in the 1960s, the savings rate was low mainly due to low rates of productivity and population growth. A merged model or a less simplified model adds to the set of variables that influence saving, for example a change in family size over the life cycle, bequests and labor supply (based on elasticity). The beauty of this model seems to be that its results hold true regardless of the variables considered.