Increase in contraceptive use, hence parents have the ability to conveniently space their children.Improvement in female education, thus women spend a lot of their fertile years in school, resulting in fall in the average number of children they can have in their lifetime.
This means there is no need to have many children in the hope that if some die others will survive. Improvement in medical care, hence low infant mortality and higher chances of babies surviving.In Kenya, the average household size fell from 5.3 persons per household in 1969 to 4.0 in 2014, concurrent with total fertility decline from 8.1 to 4.4 live births per woman (United Nations). In France, the average household size fell from 3.1 persons per household in 1968 to 2.3 in 2011, at the same time that the total fertility rate fell from 2.6 to 2.0 live births per woman. The largest household sizes were found in Senegal and Oman, averaging 9.0 and 8.0 persons, respectively ( United Nations). Large average household sizes of greater than five persons per household, were observed across much of Africa and the Middle East.
According the United Nations Report on family sizes, smaller household sizes (fewer than three persons per household) are found in most countries of Europe and Northern America, Asia and the Caribbean.