IQ differences between siblings

IQ differences between siblings are not meaningful
IQ differences between siblings are not meaningful

Researchers at the University of Illinois have published the results of the largest-ever “within family” evaluation of IQ and personality difference among siblings. The study helps shed light on IQ differences between siblings.

This very large sample study (backed by the National Institute on Aging which is part of the National Institute of Health) looked at 377,000 high school students and evaluated IQ differences between siblings, as well as differences in personality which might be influenced by the chronological order of birth.

The results of the study are clear: IQ differences between siblings are in fact influenced by birth order. First-born children on average will have a statistically significant one IQ point advantage relative to their younger siblings. Although the IQ differences between siblings are statistically significant, they are hardly meaningful as a one point IQ differential cannot produce any perceptible differences in intelligence or cognitive ability.

The study found that first-born children tend to be more outgoing and conscientious, in addition to have slightly higher IQ scores on average.

IQ differences between siblings:’s take on the study

At, we believe (based on several comprehensive studies on IQ and intelligence) that genetics factors explain the majority of the variance in IQ scores generally. However, we do acknowledge that environmental factors may have an influence on IQ scores and cognitive ability generally. Here is our analysis on the study measuring IQ differences between siblings.

On the one hand, older siblings will tend to get more parental attention and contact than their younger siblings. First-time parents are probably more likely to be more cautious with their first child (e.g. maternal contact and attention, which have been shown to increase IQ – see breastfeeding post IQ and breastfeeding). In support of the findings, older children will also need to “figure it out” as they progress through life, learning by trial and error.

The contra argument is that younger siblings, if the age gap is not too large, will tend to play and learn from older siblings, resulting in a transfer of knowledge from the older sibling to the younger one. This accelerated learning could also be an IQ booster for younger siblings, allowing for ‘catch up’ to take place.

Importantly, the IQ differential of one point, although statistically significant is not material. Based on the above two arguments however, it would be interesting to drill down into the results to test whether older siblings display a higher level of fluid intelligence (as they “figure it out”) relative to younger siblings, who are more likely to use their sequential processing and crystallized intelligence to follow in the footsteps of their older siblings.

article provided by a leader in online fluid IQ testing.

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