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Research Shows Birth Order and Family Size Are Irrelevant to Intelligence Scores and Other Characteristics

Updated on May 8, 2019
Patty Inglish, MS profile image

Patty has advanced degrees in preventive medicine and health psychology, with 35 years of work in allergy and other autoimmune treatment.

The obsolete notion of the effects of birth order on IQ, personality trait, and success has been debunked in the early 21st century.
The obsolete notion of the effects of birth order on IQ, personality trait, and success has been debunked in the early 21st century. | Source

Political Misapplication of IQ Data

For past political purposes, some researchers used skewed findings of The Bell Curve to denigrate African Americans by using the book's data to label these individuals and all persons of color as "slow", "less intelligent", "retarded" and several other inaccurate slurs. College classrooms and rigorous research of the late 20th and early 21st century have corrected this propaganda.

Unfortunately, such superstitions as the phantom effects of race and birth order on IQ and potential success persist in parts of America.

Misinterpretation of the bell curve plot of human IQs proliferated for decades, likely because it reinforced a false narrative to which some Americans clung. The persistence of belief in Birth Order Theory (BOT) is waning, but persists for the same reason.

Oh, he can't help it, he's a middle child!

— An excuse made by a parent about her child's inappropriate behavior to me in family therapy.
Source

What Is a Family Today?

The body of research studies targeting birth order are outdated, incorrect, and thus, inapplicable.This is due in part to the changing structure of the American family since the 1980s and the rise of Generations X and Y.

Families today can be traditional, blended, single parents, two-moms, two-dads, large foster groups, kibbutzes, communes, and nearly anything you can imagine. This dissolved the former standard of BOT, because it applied to traditional two-parent families.

Birth Order Theory and similar pitches have become irrelevant pop psychology.

As long ago as 1965, birth order and family size were debunked as variables that cause differences in IQ. In reality, neither variable has any effect.

This (Birth Order theory) is a pop psych thesis that’s sold a lot of books and filled a lot of talk show time, and many have assumed that it’s solid science. But according to the results of the largest study ever conducted on birth order and personality, it’s all much ado about nothing.

— David DiSalvo, Forbes; about Damian et.al. study

Changes Among Generations X, Y and Z

From the Lost Generation to Generation Z, we see that the family looks significantly different on average than it did in the ideal of the 1950s and early 1960s. Back then, the perfect image was that of a father, mother, brother, sister, cat, dog, house, car, and garage. The ideal was seen in grocery shopping ads, insurance commercials, billboards, posters in doctor's offices, and textbooks.

Add the LGBTQA+ populations that are not strictly male and female into the definitions of the modern family, and that family is alien to folks who accept only the mother-father-child ideal. it might be scary. BOT is a handle to hold to maintain the safer past.

In children's cartoons today, the family is called "the herd" and shows diversity of animal species as a proxy for diverse humanity. Further, a herd may comprise just one person or a person and a pet. This is frightening to some folks.

Birth Order Theory and similar pitches have become irrelevant pop psychology.

Source

Political Misapplication of IQ Score

Since the turn of the 21st century, after the successes of the Clinton Era Welfare to Work (W2W) programs that removed thousands of individuals from American public assistance rolls into gainful employment, some interest groups are still unhappy. They dislike the number of people of color, people of lower income, and refugees in the USA and wish to reduce their number.

IQ labeling is one method of targeting individuals for elimination. Hate groups in America suggest that large families produce low-IQ children, therefore the parents (specifically the females) should be sterilized. This was actually proposed in the Ohio legislature in 1965 when the welfare programs of President Lyndon Johnson took effect, and the Ohio proposal failed.

First IQ Test, Haslingden Health Centre -- Why was prize money awarded to the person with highest IQ Score?
First IQ Test, Haslingden Health Centre -- Why was prize money awarded to the person with highest IQ Score? | Source

Sponsor of IQ Testing Was a Businessman

Sir William Mather (1838 – 1920) was a British mechanical engineer and textile manufacturer, and Liberal politician who served in the House of Commons. As a company owner, he reduced the work day to eight hours for his employees and was most interested in education.

Historical Bias in IQ Labeling

The wish for reduced numbers in the target groups seems akin to the wish behind the staging of the Irish, Scottish, and Welsh Potato Famines that eliminated from the UK certain populations that the Crown and nobility deemed slow, less intelligence, inarticulate, drunk, shiftless, and worthless. I know this from experience.

Personal and Family Experience

In the early 1800s my father's family in the UK were British and resided in England. Seeking a better economic life, a large portion moved to - off all places - Ireland and Scotland, but quickly sailed to America when they they saw the Potato Famines gearing up to sell potatoes abroad clear the lands of people in favor of sheep and such.

Unfortunately, the emigres brought with them a stereotypical hate of the Irish and Catholics that lasted until the late 20th century.

Today's Undercurrents of Labeling and Discrimination

Currently, a few hold-out groups use Birth Order and IQ/Family-Size predictions politically to convince the public of the inherent evil of reproducing too often and of having more than one or two children per couple (or singleton).

The smallest group among the few mentioned wishes for 0 Population Growth among the "unworthies" - no reproduction at all, with a wish to have everyone who is or will be receiving public assistance cash benefits, SNAP food assistance, and/or Medicaid surgically sterilized.

As a child in 1965, when the national Public Assistance system and Medicaid were instituted under the Great Society of President Lyndon Johnson, I saw Ohio legislators propose the enforced sterilizations mentioned in the paragraph above. The legislation died in committee, because it would be too hard to enforce and likely unconstitutional.

Families have changed compositionally, but are still of various sizes.
Families have changed compositionally, but are still of various sizes. | Source

Debunking Incorrect Results of Birth Order and Family Size Studies

The first study to debunk the effects of borth order and family size on IQ scores was performed long ago in 1965.

  • "Comparisons of Mental and Motor Test Scores for Ages 1-15 Months by Sex, Birth Order, Race, Geographical Location, and Education of Parents." Nancy Bayley. Child Development Vol. 36, No. 2 (Jun., 1965), pp. 379-411.

A sample of infants representative of the US population in 1965 were administered the Bayley Scales of Mental and Motor Development in 12 major cities to 1409 infants of ages 1-15 months.

The results showed no differences in scores between

  1. Boys and girls
  2. First-born and later-born
  3. Education level of either parent
  4. Location (geographic) of residence

Final Results

  • No differences were found between African Americans and whites on the Mental Scale, but the black babies consistently scored higher than whites on the Motor Scale.
  • Puerto Ricans scored equally with whites on both scales.

More Recent Research 2000 - 2015

Previously held beliefs about birth order and IQ related to Family Size were debunked beginning in 2000, particularly in the following study and follow-on:

  • "Resolving the debate over birth order, family size, and intelligence." Rodgers, Joseph Lee; Cleveland, H. Harrington; van den Oord, Edwin; Rowe, David C. American Psychologist, Vol 55(6), Jun 2000; American Psychological Association presentation by Joseph Lee Rodgers, 2015.

The material points out serious flaws in the studies whose findings presented and reinforced the beliefs previously held related to birth order and IQ/family-size. The absolute effect size of some of these studies was found by the Rodgers group to be only 0.01 and 0.02, where 100.00 means total relatedness and 0.00 means no relation. The significance of those small numbers is "0.00" or no relation found.

Other troubling elements were discovered as well and are available in the journal article online or in your local university library.

The Rodgers Results

  • Although low-IQ parents have been making large families, large families do not make low-IQ children in modern U.S. society. The apparent relation between birth order and intelligence has been a methodological illusion.

A Scientific Amen

In 2015, the largest study into birth order was conducted, reinforcing the Rodgers findings:

  • "The associations of birth order with personality and intelligence in a representative sample (377,000) of U.S. high school students." Damian, Rodica Ioana and Roberts, Brent W. Journal of Research in Personality. Elsevier; October 2015.

The Damian Results

  • The average absolute association (not a significance score) between birth order and personality was .02 (negligible or none)
  • The average absolute association between birth order and intelligence was .04 (negligible or none)
  • Controls were age, sex, sibship size, socioeconomic status, and family structure/size.
  • The effects did not differ across different social categories.
  • "It’s tempting to credit and blame a child’s personality traits, characteristics, and fate on birth order. The reality however is so much more complex; each child’s character and fate are based on biology and environment and encompass hundreds of thousands choices in and out of his control."

Birth order probably should not influence your parenting because it’s not meaningfully related to your kid’s personality or IQ.

— Scientist Rodica Damian
Inaccuracies of Past Research Corrected
1. Families having more than two children, or many children, no longer indicates low parental IQ Scores.
2. The children in larger families indicated in Number One above no longer are destined to have low IQ Scores.
2. Birth Order is no longer (was perhaps never) linked to IQ Score.

It has been tempting to credit or blame child and adult personality traits, characteristics, and fate on birth order. Rather, each child’s personality and success or lack of it, are based on biology and environment and encompass hundreds of thousands choices in and out of his/her control.

— Damian et.al.

Obsolescence and the Future

Prior to the 20th century, personalities and intelligence were determined by feeling the bumps on the head (phrenology) of a client, patient, or accused law breaker; and by examining unrelated physical attributes like beady eyes, jaw size, high or low ("ape-like") foreheads, and physical stature depicted as endomorph, mesomorph, and ectomorph.

None of the above officially accepted procedures of the past are condoned today, because they proved incorrect. Birth Order Theory is outdated and not useful today - it is incorrect now.

Size-of-family intelligence theories are incorrect today, used to lobby governments to institute mandated birth control and abortion among minority populations.

Entertainment: Briant Hall, otherwise known as Dr. Quackenbusch the phrenologist, examined heads of those visiting the California Trail Interpretive Center while lying on a bed of nails.
Entertainment: Briant Hall, otherwise known as Dr. Quackenbusch the phrenologist, examined heads of those visiting the California Trail Interpretive Center while lying on a bed of nails. | Source

It appears that although low-IQ parents have been making large families, large families do not make low-IQ children in modern U.S. society. The apparent relation between birth order and intelligence has been a methodological illusion.

— Rodgers, et.al.

Skin color and other demographics were added for diagnosis of low IQ in the past, but were incorrect. The Reverend K.C. Price broadcast months of televised presentations about this error from his church in Los Angeles, California in the 1980s and 1990s. People are finally listening ion the 2010s.

The film BlacKkKalansman (2018) strongly illustrates how false theories were used to condemn Blacks and Jews as low-IQ, dishonest, and non-human creatures as late as the 1970s. Many hate groups exist in America and I hope to see them disintegrate along with the incorrect intelligence theories we still see operating in error.

Sources

  • Bayley, N. Comparisons of Mental and Motor Test Scores for Ages 1-15 Months by Sex, Birth Order, Race, Geographical Location, and Education of Parents. Child Development Vol. 36, No. 2 (Jun., 1965), pp. 379-411.
  • Damian, R. I. and Roberts, B. W. The associations of birth order with personality and intelligence in a representative sample (377,000) of U.S. high school students. Journal of Research in Personality. Elsevier; October 2015.
  • Inglish, P. Equipped for the Future Standards. hubpages.com/education/Equipped-For-the-Future-Standard-Abilities-For-Adults-Ages-21-and-Older Retrieved August 19, 2015.
  • Rodgers, J. L.; Cleveland, H. H.; van den Oord, E.; Rowe, D. C. Resolving the debate over birth order, family size, and intelligence. American Psychologist, Vol 55(6), Jun 2000; American Psychological Association, 2014. Retrieved August 23, 2015.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2015 Patty Inglish MS

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