Only since drop in fertility and rise in mortality. Result is that households structures vary across times as children are born, mature, and leave the house. Intactness of marriage, age of householder, and age of children all effect the likelihood that a family will own their own house or live in rental housing. The trends in the Untied States are generally comparable to other developed countries, particularly those in the West. Nevertheless, the general trends we have discussed are most related to the demographic transition which is part of general economic development.
Mortality rates are lowest in Japan and Scandinavia.
Because they also have good public health systems, mortality is lower with the consequence that family sizes are larger, and growth rates very high. These countries tend to have a pro-natalist philosophy which emphasizes separation of the sexes, and women bearing children. Iraq is also seven children per woman, although it does not fit easily into a category of being extremely poor, or developed. The poorer countries also tend to have higher mortality rates. Nevertheless, is still a useful measure.