When it comes to the ideal family size, bigger may not be better.

According to Stuff, brand new research has revealed that “every additional child born to a family increases their siblings’ chances of developing behavioural issues, lower cognitive abilities and overall, having worse outcomes later in life.”

The research, titled ‘The Quantity-Quality Trade-off and the Formation of Cognitive and Non-cognitive Skills’, was based on 26 years worth of data and it was written by three economists, Chinhui Juhn, Yona Rubinstein and C Andrew Zuppann.

The gist of the US-based research is that smaller families lead to a greater level of "parental investment" in each child - which was measured by factors such as how often families ate together, how often parents showed affection to their kids and how many books each child had access to.

The research suggests that parental investment helps to determine a child's future "level of education, employment status as adults and general status in society".

For every additional child that is born, the parental investment will drop by three per cent. Cognitive ability will drop by 2.8 per cent and behavioural problems will increase.

The study also examined gender, genetics and socio-economic factors and found that mothers with a higher cognitive ability would have more successful children.

It's fascinating food for thought...and more than a little worrying for those of us who come from larger families.

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