This was reinforced by important social trends, the reduction in average family size meant that many parents could devote more time to each of their children. (sciencedaily.com)
Smaller average family size — 2.5 people today versus 2.9 people in 1973 — explains part but not all of the difference. (rismedia.com)
In California, both NME and pertussis clusters were associated with factors characteristic of high socioeconomic status such as lower population density; lower average family size; lower percentage of racial or ethnic minorities; higher percentage of high school, college, or graduate school graduates; higher median household income; and lower percentage of families in poverty. (pediatrics.aappublications.org)