A study has found having a "bigger family" puts children at risk of developing behavioral issues and lower cognitive abilities, which could lead to problems later in their adult life. Three economists analyzed 26 years' worth of data on parents and their children and found that the difference in number of children results in a "trade-off" between quality and quantity.

The term "quality," despite its awkwardness, refers to several factors such as the quality and level of education each child receives and finishes, employment feasibility in adult life and the possibility of ending up with a criminal record. The new study supports the current and widespread theories that the amount of time and resources parents invest in early child development have life-long effects and rewards.

The Study

C. Andrew Zuppann, Chinhui Juhn and Yona Rubinstein looked at the 1979 National Longitudinal Survey of Youth data set. The survey asked families about their children's behavioral issues as well as their reading and math abilities. The survey also focused on home environment factors such as the amount of time parents' helps kids with their homework or if they read to them.

The research team measured how older kids performed before and after the birth of younger siblings. The team measured "parental investment" by looking at how often families ate meals together, how many books each child has or how often parents display affection to their children.

Interestingly, the team has found that "parental investment" dropped 3 percentage points after the birth of a younger child. Coincidentally, a child's cognitive score also dropped 2.8 percentage points after the birth of a younger sibling. The child's rate of behavioral problems likewise increased.

Gender played a role in the change. The team found that math and reading scores of girls with younger siblings suffered more compared to boys who gained younger siblings. However, the latter were more susceptible to having behavioral issues.

For every addition of a younger child, the average amount of education received by all kids in the family dropped by -.13 years. The situation is far worse for older kids who have younger twin siblings. In these families, children often end up with almost half a year less of education received.

"On average, children in larger families have lowered parental investment and worse cognitive and non-cognitive outcomes," said [pdf] the researchers.

The study has demonstrated that these are not temporary effects following the birth of a younger child and the findings have proved true throughout childhood and expanded into adult life. These ill effects resulted in less education, lower earning capacity, increased criminal behavior and even teenage pregnancies.

The research was published in the U.S. National Bureau of Economics Research website in December 2015.

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