A new study, based on a large, nationwide sample, suggests a critical flaw in that previous research which says that older children are more intelligent than younger ones.
This was said by Aaron Wichman, lead author of the new study and a teaching fellow in psychology at Ohio State University.
Aaron Wichman said, "Third- and fourth-born children all come from larger families, and larger families have disadvantages that will impact children's intelligence. In reality, if you look at these larger families, the fourth-born child is just as intelligent as the first-born. But they all don't do as well as children from a smaller family."
collaborators were Joseph Lee Rodgers of the University of Oklahoma and Robert MacCallum of the University of North Carolina-Chapel Hill and professor emeritus of psychology at Ohio State. Their findings were published in a recent issue of the journal Personality and Social Psychology Bulletin.
The new study used data involving nearly 3,000 families from 1986 through 1998 who participated in the National Longitudinal Survey of Youth, which is funded primarily by the U.S. Bureau of Labor Statistics. The NLSY is a nationally representative survey of people nationwide conducted by Ohio State's Center for Human Resource Research.
The researchers compared intelligence test results at two specific age points (7-8 years old and 13-14 years old). Other studies had examined how children in a family scored on intelligence tests taken at one time, when children's ages may vary widely. This may have affected study results.
Researchers examined the data initially while ignoring environmental influences on intelligence that differed between families. Then came another parameter mother' age.
"Mother's age encapsulates many variables that could negatively effect the child-rearing environment. The younger a mother was at the birth of her first child, the lower we would expect intelligence scores to be within a family," Wichman said.
Results of the study are:-
"Birth order may appear to be associated with intelligence, but that's only because larger families don't have the advantages of smaller families," he said. "When examined within families, there is no evidence of any significant association between birth order and intelligence. It's not your birth order that is important - family environment and genetic influences are the really important factors."