Why do children in larger families tend to have lower intelligence than children with fewer siblings?

Question

"the tendency for large families to produce lower IQ children holds regardless of the research approach (Rodgers, et al., 2000)"

from http://www.indiana.edu/~intell/birthOrder.shtml

"Our results suggest that earlier born children have higher IQs, and this effect becomes slightly larger when controls for birth characteristics are included, suggesting that it is unlikely that biological explanations for birth order effects play much role. In addition, we find that family size has a negative effect on IQ, suggesting that random shocks to family size have a negative
effect on existing children."

from http://paa2007.princeton.edu/download.aspx?submissionId=71094

...and of course Google can find you many more research studies on the topic...

(Don't bother with the "IQ tests don't measure anything" argument--that's as good as saying you haven't read anything about intelligence and IQ tests. I'm afraid these research results are quite real.)

I wonder...

What's the best way to respond to people who have several research studies staring them straight in the face (that they won't look up and read or bother to intelligently critique) who claim they won't believe the findings because--why else?--the findings make them feel bad?

Answer 1

I guess because the children from smaller families have more time spent to them early in development and get more attention to their education. Unless your a super mom, its hard to equal out every childs need in every area. Just a guess, but it makes sense to me.

Answer 2

Sheesh. I don't know how you can keep on with this nonsense when it's obviously "Not True @ All!!!!!" because "My 5 yr old can count to 50 and has been reading for 3months." (Three _years_, I'm listening, but...yikes.)

I have no cite for this, but. I very vaguely remember reading about some deleterious effects of pregnancies spaced too closely together. In lay terms: don't give your body time to recover, and it'll do a sloppy job, sometimes.

Quite inexplicably, though, that same study offered an 'ideal' wait time between children. I think it was 2-5 years. For some reason, things started to go downhill again after five years. Very curious.

However:

"Abstract: Investigated the relationship between birth order, family size, and intelligence quotient (IQ), evaluating sibling data from the National Longitudinal Survey of Youth and comparing results with those from other studies using within-family data. Results indicated that although low IQ parents were making large families, large families were not making low IQ children. Similarly, the belief that birth order affects intelligence is a methodological illusion."

http://eric.ed.gov/ERICWebPortal/custom/portlets/recordDetails/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=EJ627449&ERICExtSearch_SearchType_0=eric_accno&accno=EJ627449

That "low IQ parents were making large families" part would be much more fun to drag Mrs My Five Year Old Can Look At Picture Books So You're Wrong!! types out of the woodwork here...

More 'math's bad, there's no relationship' about what you're citing here:

http://links.jstor.org/sici?sici=0003-1224(199104)56%3A2%3C141%3ABOAIFT%3E2.0.CO%3B2-0

Answer 3

Not True @ All!!!!!

My Fiance Is The Oldest Of 7 Kids And Most Of Them Are Smart... The 10 Year Old Boy Is 2 Grades Ahead Of Kids His Age And The 15 Year Old Is An Honor Holl Student... The 6 Month Old Already Says "Dada"

A Friend Of Mine Also Has 5 Boys... The Middle Child Is 8 And Is In The Same Grade As His 10 Year Old Brother...
I Think It's A Myth... Just Depends On The Family And How Much The Parents Are Willing To Teach Their Children...

Answer 4

Are you an only child and are bitter and jaded because of it? I just read your other question about large families. What gives?

My great grandmother is one of 14 children, and she (and her siblings who are still alive) are some of the most intelligent, caring, wonderful people I've ever met.

The low IQ/doing poorly in school could also be said for inner-city blacks who live in the ghetto. Why not go to the Society and Culture board and post this question there and single THEM out, instead of people who happen to love children and want a large family?

You're unbelievable--coming here to the Pregnancy and Parenting section asking a loaded question and then having the nerve to become offended and attack people when you receive answers you don't like. What the hell is wrong with you? Oh, I got it! You're the youngest of 10 children, aren't you? I guess you were right--children of large families ARE unintelligent.

Have a great day! :)

Answer 5

What do you mean by a larger family? People used to have 6 - 12 children but now 3 or 4 children is considered a large family. I have 3 children who are all very intelligent. My oldest daughter even graduated a year early. So, I would define large family and then look up case studies.

Answer 6

Quite simply you are wrong about that.

http://www.medscape.com/viewarticle/411957

"Contrary to popular belief, having more children born into a family does not necessarily result in lower-IQ children, according to new research published in the June issue of American Psychologist.
In their study, Joseph Lee Rodgers, PhD, of the University of Oklahoma, and colleagues looked at data from the National Longitudinal Survey of Youth (NLSY), a large random national sample of families that included children whose academic performance had been reviewed multiple times throughout their academic careers. The NLSY originated in 1972 as a household probability sample of the nation's youth aged 14 to 22 years. For 22 years, the sample followed 11,406 young people at yearly intervals. Starting in 1986, the children born to the original female respondents were surveyed every other year. The family structure measures and intelligence scores of these children provide the basic data used in this study.

The relationships among family size, birth order, and intelligence have been the subjects of much earlier research. However, most of that previous research has been limited by problems of evaluating within-family models using only across-family measures. For example, family size is an "across-family" measure, while birth order is a "within-family" measure. According to the authors, earlier research on the issue of a link between birth order and intelligence lead to spurious conclusions, one of them being an apparent link between both birth order and offspring intelligence and family size and offspring intelligence. These "links," according to the authors, were caused by mistaking across-family effects for within-family effects.

"There are many good reasons why parents might consider limiting their family sizes, but the belief that, for a particular set of parents in a modern country like the United States, a larger family will lead to children with lower IQs appears to be, simply, wrong. The belief that birth order acts directly to decrease the intelligence of children born later in a given family also appears to be, simply, wrong," state the authors."

.

Answer 7

I have mixed feelings about this. I'm guessing that it probably relates (at least partially) to the amount of time the parents have available to do things like read to their children. I have a friend who has four kids, which I guess would be considered a fairly large family nowdays. Her first two kids are brilliant, and the younger two are far from it. But I have three children (I'm a single Mom) and I would say that my youngest is actually MORE advanced academically than my oldest. So I guess it really depends on the situation.

Answer 8

Anecdotally, my own experience does not bear this out. There are 7 kids in my family and at least 4 of us have IQs in the genius range and the other 3 are far from stupid.

Maybe the researchers have the cart before the horse: maybe the majority of people who have lots of kids aren't that bright to begin with...and the smarter people know better than to have more kids than they can afford to raise and educate...

Answer 9

i have 3 children and don't agree with this study either. My son is 12yrs old and has just taken the SAT( he is in the Duke University, program, he scored a 1350) and is a straight a student, My 5 yr old can count to 50 and has been reading for 3months, and my 2yr old can count to 25, say her abc's and knows her colors. We always made an effort when it was homework time to have it be a family thing so everybody had a task when my son did his homework.......maybe this helps

Answer 10

I think this is crap. I am number 3 of 6 children in my family. My two older siblings and myself have graduated from universities (Duquesne, Penn State, Juliard) have great jobs and a wonderful family life. My three younger siblings are still in school but are in the honors/AP track and are doing wonderfully. I married an only child and I don't feel that I am his inferior in intellect. I think you put this question in yahoo answers to piss people off.