“Birth order and it’s effects on the person has been fascinating scientists and the general public for at least one hundred years,” says Janice Weddle, County Engagement Specialist in Youth Development for the University of Missouri Extension.  There have been several studies to try to pinpoint birth order effects on intelligence and personality, but results are met with criticism due to many factors, like the confounds of the research or the method used in the research. 

 “Confounds of a research study are variables that are not being measured in the research but could alter the results,” said Weddle.   There are two methods of study when examining birth order effects, within-family and between-family.  A between-family study design examines unrelated families and a within-family study design while a within-family study examines the personalities and intelligence of children within the same family.  

“Depending on the confounds and methods of the study, results can vary greatly in research on birth-order effects.  It is important to understand the full scope of any study before taking the results to the bank,” said Weddle.

Common hypotheses from both the general public and scientists for birth-order effects are that first-born children tend to be smarter and more conscientious while later-borns tend to be more agreeable and social.  Common confounds when studying birth order include sibship (i.e. family) size, parental socioeconomic status, family structure, age, and gender. 

“Some of the confounds that are also noteworthy are things like large age gaps between siblings, and non-biological family structures,” says Weddle.    Also important in birth-order research is the method, between- or within-family.  Results do generally stay consistent when using between-family or within-family study designs. 

Some research concludes that there are extremely slight correlations between birth order and intelligence, and of these the results show that intelligence and educational attainment decrease with birth order. One study also found that both first-borns and later-borns report that the later-born sibling tends to be the family rebel. 

There is not conclusive empirical evidence suggesting that birth order has a significant impact on personality or intelligence.  Research has not consistently proven the common hypotheses of first-borns being smarter and more conscientious and later-borns being more agreeable and social.  In many cases, these common hypotheses are contradictory to popular belief.    

Due to the only partial and slight correlation of birth-order effect on intelligence and personality, and because of many family dynamics creating confounds that could impact results, research has not found a correlation large enough to say that birth order consistently has any magnitude on personality or intelligence.

 “Many people have their opinions on birth-order effect on a person. Most everyone has heard of middle-child syndrome. Interestingly, in many studies the first- and middle- born siblings rank equal between parental favoritism.  We all have our own sort of personal case study of birth-order effects under our own roofs, and I think that is what makes this topic so fascinating as the opinions and expectations can vary greatly,” said Weddle.

4-H offers many opportunities for youth to find their place, discover their value, and feel a place of belonging.  4-H also creates an atmosphere for families to spend time together and create lasting memories.  For more information on 4-H programs in your county contact County Engagement Specialist in Youth Development, Janice Weddle, at the University of Missouri Extension Office in Mountain Grove at 417-349-4134 or via email at