Some observers attribute nearly all of the world 's maladies to excessive population growth. They claim that rapid population growth has at least three adverse effects on human well-being. First, it increases poverty--the number of people that are impoverished, the proportion of the community that is impoverished, and the severity of the impoverishment. Second, it increases environmental degradation--the misuse of natural resources--with adverse consequences on many dimensions of human well-being. Finally, it prevents environmental enhancement by holding back the savings and investment that would permit environmentally sustainable economic growth and retards the agricultural productivity that would encourage environmentally friendly agriculture and conservation (Ahlburg 1994; Kelley and McGreevey 1994).
These contentions, however, are not necessarily accurate. The adverse effects of population growth can easily be confused with other factors, because rapid population growth often occurs along with other forces that reduce human well-being (Kelley 1988; Panayotou 1994). For example, rapid population growth is common in many tropical areas of the world. Yet tropical environments themselves retard human productive activity due to heat, endemic disease, and poor soils (Sachs and Warner 1997). It would be easy to conclude that fast population growth lowers productivity, when actually the tropical environment may be the cause.
In such cases, where multiple factors determine various outcomes and it is difficult to distinguish cause and effect, multiple regression analysis is a useful tool. It allows us to examine the effects of population growth simultaneously with the effects of favorable economic institutions and other possible explanatory factors. Essentially, we are holding the other factors constant so that we can measure the sensitivity or elasticity of one factor or variable (such as access to safe water) to the change in