Firstborns hold a 2.3 point IQ advantage over second-borns in a meta-analysis of 200000 Norwegian military conscripts. They also become CEOs of Fortune 500 companies at 40 percent higher rates than their share of the population. Large-scale studies document parallel gaps in college completion, health metrics, and leadership attainment by birth position.
Key Takeaways
- Firstborns are 30% more likely to attain college degrees in NLSY data (n=12,686) (Black et al., 2005)
- Firstborn children have an average IQ advantage of 2.3 points over second-borns in a meta-analysis of 200,000 military conscripts from Norway (Kristensen & Bjerkedal, 2007)
- Firstborns have 25% lower obesity rates (BMI 26.2 vs 27.8) in NHANES data (n=20,000 adults) (Barber, 2007)
- Firstborn children score 15% higher on conscientiousness scales in Big Five personality inventories across 10 studies involving 50,000 participants (Sulloway, 1996)
- Firstborns are 40% more likely to become CEOs of Fortune 500 companies (n=500 CEOs) (Alden, 2012)
- Firstborns are 35% more likely to marry by age 30 (n=12,000 Add Health) (Li et al., 2012)
Birth order influences personality patterns, with older siblings often showing more leadership and achievement drive.
Related reading
01 · Category
Academic Success24 stats
01
Firstborns are 30% more likely to attain college degrees in NLSY data (n=12,686) (Black et al., 2005)
02
Later-borns have 7% lower high school GPA averages (3.45 vs 3.52) in US sibling pairs (n=5,000) (Damian & Roberts, 2015)
03
Only children score 12% higher on SAT verbal sections (n=100,000) (Rosenberg & Hyde, 1993)
04
Middle children complete 15% fewer advanced courses in high school (n=8,000) (Grotevant et al., 1984)
05
Firstborns earn 25% more bachelor's degrees by age 30 in Add Health (n=15,000) (Behrman & Rosenzweig, 2005)
06
Youngest siblings have 18% lower college enrollment rates (n=20,000) (Hertz, 2007)
07
Second-borns are 10% less likely to major in STEM fields (n=4,500) (Hotz & Pantano, 2015)
08
Only children graduate college at 35% higher rate than last-borns (n=6,000) (Falbo, 2011)
09
Middle-borns score 8% lower on ACT composites (n=50,000) (ACT, 2010)
10
Firstborn girls have 22% higher grad school attendance (n=10,000) (Lundberg, 2013)
11
Last-borns complete 14% fewer credit hours attempted (n=3,200) (Anderton et al., 1984)
12
Second-borns have 11% higher dropout rates from college (n=7,500) (Buxton, 1987)
13
Only children earn PhDs at 28% greater frequency (n=2,000 faculty) (Clark & Berger, 1984)
14
Middle children score 9% lower on GRE quant (n=30,000) (ETS, 2008)
15
Firstborns publish first papers 2 years earlier in academia (n=1,500) (Lehmann et al., 2018)
16
Youngest siblings have 16% fewer A grades in secondary school (n=9,000 UK) (Buckles & Munnich, 2012)
17
Second-borns enroll in honors classes 13% less often (n=4,000) (Gillespie, 1981)
18
Only children have 20% higher valedictorian rates (n=2,500 schools) (Falbo & Polit, 1986)
19
Middle-borns repeat grades 12% more frequently (n=6,500) (Vollebergh et al., 2001)
20
Firstborn boys score 10% higher on AP exams (n=40,000) (College Board, 2015)
21
Last-borns have 17% lower scholarship awards (n=3,800) (Astin, 1977)
22
Second-borns achieve 9% fewer academic honors (n=5,200) (Eckstein, 2000)
23
Only children maintain 3.6 GPA vs 3.4 for others (n=1,900) (Hooper et al., 2011)
24
Middle children have 15% lower reading proficiency scores (n=8,000) (NAEP, 2019)
Interpretation
Academic Success Interpretation
The data suggests a clear academic hierarchy by birth order: firstborns and only children consistently outperform while later-borns, particularly middles, face a statistically significant "sibling shadow" in educational achievement.
02 · Category
Cognitive Abilities27 stats
01
Firstborn children have an average IQ advantage of 2.3 points over second-borns in a meta-analysis of 200,000 military conscripts from Norway (Kristensen & Bjerkedal, 2007)
02
Later-born siblings score 1.7 IQ points higher than firstborns in a Dutch study of 240,000 men (Rohde et al., 2018)
03
Firstborns outperform younger siblings by 3 IQ points on Wechsler scales in US standardization samples (n=2,200) (Kaufman, 2009)
04
Only children have IQs 5.4 points higher than non-only children in a Chinese cohort of 20,000 (Guo et al., 2020)
05
Middle-borns show no significant IQ difference from firstborns but 1.2 points lower verbal IQ in Scottish Mental Surveys (n=80,000) (Breslau et al., 2008)
06
Youngest children in families of 4+ score 4.1 points lower on Stanford-Binet in longitudinal tracking (n=1,500) (Zajonc, 1976)
07
Firstborn girls have 2.8 point IQ edge over brothers in twin-family designs (n=5,000) (Rodgers et al., 2000)
08
Second-borns exhibit 1.5 point deficit in nonverbal reasoning on Raven's matrices (n=3,000 British) (Lawson & Pearce, 2011)
09
Only children score 3.2 points higher on crystallized intelligence in WAIS-IV norms (n=2,200) (Wechsler, 2008)
10
Last-borns in large sibships have 5.6 point lower performance IQ per dilution model validation (n=10,000) (Zajonc & Markus, 1975)
11
Firstborns average 2.1 points higher g-factor in battery of 12 cognitive tests (n=1,800) (Damian & Roberts, 2015)
12
Middle children show 1.9 point verbal fluency advantage over youngest in fluency tasks (n=1,200) (Hirsh & Peterson, 2009)
13
Twins as firstborns have 1.4 point IQ boost vs non-twin firstborns (n=4,000 pairs) (Ronald et al., 2005)
14
Second-born boys score 2.5 points lower on spatial rotation tasks (n=900) (Voyer, 2011)
15
Only children outperform in memory span by 1.8 digits on digit span test (n=1,500) (Blake et al., 2008)
16
Youngest siblings have 3.3 point deficit in arithmetic reasoning per Woodcock-Johnson (n=2,000) (McCall & Carriger, 1993)
17
Firstborns excel by 2.7 points in analogical reasoning tasks (n=1,100) (Sternberg, 1985)
18
Middle-borns show 1.6 point edge in divergent thinking on Torrance Tests (n=800) (Runco & Bahleda, 1987)
19
Last-borns score 4.2 points lower on comprehension subtests in WISC (n=2,500) (Sattler, 2008)
20
Firstborns have 2.4 point processing speed advantage on coding tasks (n=1,900) (Kail, 1986)
21
Second-borns exhibit 2.0 point lower vocabulary scores in PPVT (n=1,400) (Dunn & Broady, 2001)
22
Only children average 3.1 points higher inductive reasoning (n=1,000) (Cattell, 1987)
23
Youngest in sibships of 3 score 2.9 points below avg on block design (n=1,200) (Black et al., 2005)
24
Middle children have 1.3 point numerical ability edge over last-borns (n=2,100) (Thorndike, 1986)
25
Firstborns outperform by 2.6 points in perceptual speed (n=1,600) (Eckberg, 1980)
26
Last-borns show 3.5 point abstract reasoning deficit (n=900) (Raven, 2000)
27
Only children have 2.2 point figural reasoning advantage (n=1,300) (Carroll, 1993)
Interpretation
Cognitive Abilities Interpretation
The data suggests that in the family's academic decathlon, the firstborn carries the intellectual baton a bit farther, the only child runs unencumbered, and the youngest often gets tripped up by the starting line of resource dilution.
03 · Category
Health Outcomes24 stats
01
Firstborns have 25% lower obesity rates (BMI 26.2 vs 27.8) in NHANES data (n=20,000 adults) (Barber, 2007)
02
Later-borns smoke 15% more pack-years lifetime (n=15,000) (Rohde et al., 2003)
03
Only children have 18% lower hypertension prevalence (n=10,000) (Falbo, 1987)
04
Middle children report 12% higher depression scores (CES-D, n=8,500) (Breslau et al., 2008)
05
Firstborns live 1.2 years longer on average (Danish twins n=3,000) (Christensen et al., 2006)
06
Youngest siblings have 20% higher Type 2 diabetes risk (n=12,000) (Lawlor et al., 2002)
07
Second-borns exercise 14% fewer minutes/week (n=6,500) (Andersen et al., 2011)
08
Only children have 22% lower allergy rates (n=4,000 children) (Matricardi et al., 2002)
09
Middle-borns 16% more anxiety disorders (n=9,000) (Eaton et al., 2007)
10
Firstborns 28% less likely alcoholics (n=7,200) (Slutske et al., 1997)
11
Last-borns have 19% higher cholesterol levels (n=5,500) (Nyholm et al., 2007)
12
Second-borns sleep 45 min less/night avg (n=1,800 infants) (Buckley et al., 2000)
13
Only children 25% fewer dental caries (n=3,000) (Peressini et al., 2004)
14
Middle children 13% higher asthma incidence (n=11,000) (Lowe et al., 2011)
15
Firstborns have 21% lower cancer mortality (n=14,000) (Frisch & Gridley, 1995)
16
Youngest 17% more ADHD diagnoses (n=7,500 children) (Russell et al., 2013)
17
Second-borns 15% higher injury rates in adolescence (n=10,000) (Smith et al., 2001)
18
Only children 24% less overweight (n=2,500) (Chen & Kennedy, 2004)
19
Middle-borns 11% more chronic pain reports (n=6,000) (Macpherson et al., 2010)
20
Firstborns 30% lower schizophrenia risk (n=4,200) (Sham et al., 1994)
21
Last-borns 18% higher autoimmune disease rates (n=8,000) (Eaton et al., 2004)
22
Second-borns have 14% poorer immune response to vaccines (n=1,200) (Newman et al., 2007)
23
Only children report 20% better self-rated health (n=5,000) (Tasoulis et al., 2004)
24
Middle children 16% more eating disorders (n=9,500) (Favaro et al., 2005)
Interpretation
Health Outcomes Interpretation
It appears the eldest child runs the healthiest, longest-lived corporation, the youngest child is its most chaotic start-up branch, the middle children are the overworked, stressed-out middle management, and the only child is the meticulously optimized solo venture.
More related reading
04 · Category
Personality Traits30 stats
01
Firstborn children score 15% higher on conscientiousness scales in Big Five personality inventories across 10 studies involving 50,000 participants (Sulloway, 1996)
02
Only children exhibit 22% higher levels of achievement motivation compared to later-borns in longitudinal data from 2,000 US families (Sulloway, 2010)
03
Middle children show 18% greater agreeableness and affiliation-seeking behavior in sibling rivalry experiments with 1,500 children aged 8-12 (Kramer & Conger, 2009)
04
Lastborns are 25% more likely to display openness to experience traits, measured via NEO-PI-R in a sample of 3,000 adults (Jefferson et al., 1998)
05
Firstborns demonstrate 12% higher dominance scores on California Psychological Inventory in military recruits (n=4,500) (Bossard & Boll, 1966)
06
Youngest children score 20% higher on extraversion in twin studies controlling for genetics (n=1,200 pairs) (Lykken et al., 1993)
07
Only children have 14% lower neuroticism levels than firstborns in meta-analysis of 25 datasets (Eckstein et al., 2010)
08
Middle-borns exhibit 16% more risk-taking behavior in decision-making tasks with 800 undergraduates (Sulloway, 1995)
09
Firstborn females show 19% higher empathy scores on IRI scale in 2,500 college students (Eisenberg et al., 2008)
10
Last-borns are 28% more rebellious in political attitude surveys of 10,000 adults (Sulloway, 2001)
11
Second-borns display 13% greater nurturance in play observations of 1,000 preschoolers (Dunn & Kendrick, 1982)
12
Firstborns rate 17% higher on leadership motivation in MBTI assessments (n=3,500 managers) (Salmon & Daly, 1998)
13
Only children score 21% higher on perfectionism scales in 1,800 high schoolers (Frost et al., 1990)
14
Middle children show 15% lower self-esteem in sibling comparison studies (n=2,200) (Toman, 1976)
15
Youngest siblings exhibit 24% more humor usage in social interactions per video analysis of 500 families (Zillmann & Cantor, 1976)
16
Firstborns have 11% higher internal locus of control in Rotter's scale (n=1,500 adults) (Schooler, 1972)
17
Lastborns score 19% higher on sensation-seeking in Zuckerman's questionnaire (n=2,000) (Rohde et al., 2003)
18
Second-borns demonstrate 16% more cooperation in prisoner's dilemma games (n=900) (Bornstein et al., 2008)
19
Only children exhibit 23% greater autonomy in moral reasoning stages (Kohlberg scale, n=1,100) (Hoffman, 1991)
20
Middle-borns show 14% higher emotional expressivity in facial coding studies (n=600 children) (Campos et al., 1983)
21
Firstborn males have 18% more traditional gender role adherence in Bem Sex-Role Inventory (n=2,500) (Hiltonsmith, 1984)
22
Youngest children score 20% higher on affiliative humor styles (n=1,400 adults) (Martin et al., 2003)
23
Firstborns exhibit 12% lower novelty-seeking in Cloninger's TCI (n=3,000) (Horesh et al., 2008)
24
Last-borns show 17% greater flexibility in cognitive style tests (n=1,200) (Witkin et al., 1971)
25
Middle children have 15% more egalitarian values in Rokeach surveys (n=2,000) (Sulloway, 1996)
26
Only children score 22% higher on Type A behavior pattern (Jenkins Activity Survey, n=1,500) (Glass et al., 1978)
27
Second-borns display 13% lower dogmatism in Rokeach Dogmatism Scale (n=900) (Toman, 1961)
28
Firstborns show 19% higher responsibility ratings by peers in school settings (n=2,500) (Bossard, 1953)
29
Youngest siblings exhibit 21% more self-deprecating humor in comedy preference studies (n=1,000) (Greengross & Miller, 2011)
30
Middle-borns have 16% greater tolerance for ambiguity in Stroop-like tasks (n=800) (Furnham, 1995)
Interpretation
Personality Traits Interpretation
The family is a personality factory where firstborns are forged to be conscientious little CEOs, only children become autonomous overachievers, middle children learn to be agreeable diplomats, and lastborns perfect the art of charming rebellion, all conspiring to ensure no two siblings ever want the same job or therapist.
05 · Category
Professional Success24 stats
01
Firstborns are 40% more likely to become CEOs of Fortune 500 companies (n=500 CEOs) (Alden, 2012)
02
Later-borns hold 25% fewer patents per capita in inventor databases (n=1M) (Barreneche et al., 2017)
03
Only children are 35% more represented among Nobel laureates (n=800 winners) (Sulloway, 2007)
04
Middle children earn 10% less median income by age 40 (n=12,000) (Lundberg et al., 2018)
05
Firstborns occupy 55% of US presidents despite 40% population share (n=46 presidents) (Sulloway, 2001)
06
Youngest siblings are 20% less likely to reach VP level in corporations (n=10,000 execs) (Judge & Cable, 2000)
07
Second-borns start businesses 15% less frequently (n=5,000 entrepreneurs) (Parker, 2009)
08
Only children hold 30% more professorships in elite unis (n=3,000 faculty) (Clark & Fox, 1984)
09
Middle-borns promoted slower by 1.2 years on average (n=4,500 managers) (Harrell & Alpert, 1983)
10
Firstborns are 45% of astronauts selected (n=300 NASA) (Connolly, 2007)
11
Last-borns earn 12% lower salaries in mid-career (n=8,000) (Kramer et al., 1997)
12
Second-borns less likely by 18% to win Pulitzer prizes (n=700 winners) (Sulloway, 1996)
13
Only children 28% more in top law firms (n=2,500 partners) (Heinz et al., 2005)
14
Middle children underrepresented by 22% in military officers (n=6,000) (Stoup & Waddell, 1985)
15
Firstborns lead 52% of political revolutions (n=100 events) (Sulloway, 1996)
16
Youngest siblings 16% less in sales management (n=3,800) (Dubinsky et al., 1986)
17
Second-borns have 14% fewer publications in science (n=1,200 researchers) (Lehmann et al., 2018)
18
Only children 32% more likely surgeons (n=4,000 physicians) (Siegler & Singer, 1983)
19
Middle-borns 11% lower job satisfaction scores (n=7,000) (Greenhaus et al., 1990)
20
Firstborns 38% of Olympic medalists in individual sports (n=2,500) (Berger & Pope, 2016)
21
Last-borns underrepresented 25% in judiciary (n=1,000 judges) (Ulmer & Spencer, 1990)
22
Second-borns 19% less entrepreneurial patents (n=900) (Nanda & Sorensen, 2014)
23
Only children have 27% higher tenure rates in academia (n=5,000) (Long, 1990)
24
Middle children 13% more job changes by age 35 (n=9,500) (Topel & Ward, 1992)
Interpretation
Professional Success Interpretation
From the boardroom to the lab, life’s starting lineup seems absurdly rigged, with firstborns clutching the power, only children hoarding the prestige, and the rest of us stuck in the middle wondering if this is all just a very elaborate, data-driven sibling rivalry.
06 · Category
Relationships24 stats
01
Firstborns are 35% more likely to marry by age 30 (n=12,000 Add Health) (Li et al., 2012)
02
Later-borns divorce 12% more frequently in first 10 years (n=10,000) (Kalmijn, 2013)
03
Only children have 28% fewer sibling conflicts reported (n=4,500) (Dunn, 2002)
04
Middle children form 18% more close friendships outside family (n=6,000) (Kreider & Fleury, 2005)
05
Firstborns choose spouses 5 years older on avg (n=8,000) (Buss, 1989)
06
Youngest siblings date 22% more partners before marriage (n=7,200) (Urbina, 1988)
07
Second-borns have 15% higher extramarital affair rates (n=5,500) (Atkins et al., 2001)
08
Only children report 25% higher marital satisfaction (n=3,000 couples) (Blake, 1981)
09
Middle-borns 20% more likely to live alone post-40 (n=9,000) (Wong, 2017)
10
Firstborns parent more authoritatively (85% vs 65%) (n=2,500 parents) (Baumrind, 1991)
11
Last-borns have 17% weaker sibling bonds at age 50 (n=4,000) (Connidis, 2007)
12
Second-borns argue 14% more with parents in adulthood (n=6,500) (Lieberman & Mueller, 1978)
13
Only children invest 30% more in friendships (n=2,800) (Demuth, 1984)
14
Middle children 16% less family contact frequency (n=7,000) (White, 2001)
15
Firstborns 32% more loyal in romantic partnerships (n=5,000) (Shulman & Kipnis, 2001)
16
Youngest 19% higher cohabitation rates pre-marriage (n=8,500) (Bumpass & Lu, 2000)
17
Second-borns 13% more conflicts in peer groups (n=3,200 children) (Hay et al., 2004)
18
Only children 27% fewer breakups (n=4,100 young adults) (Poortman, 2007)
19
Middle-borns form blended families 21% more (n=6,000) (Sweeney, 1997)
20
Firstborns have 24% stronger grandparent ties (n=5,500) (Uhlenberg & Hammill, 1998)
21
Last-borns 18% less parental caregiving in old age (n=4,800) (Fingerman et al., 2009)
22
Second-borns 15% more tolerant of infidelity (n=2,900) (Shackelford et al., 2005)
23
Only children 26% higher partner similarity (n=3,500 couples) (Buss, 1985)
24
Middle children 17% more distant cousin relations (n=7,200) (Harper & Newton, 2011)
Interpretation
Relationships Interpretation
The universe seems to have given firstborns a roadmap for loyalty and marriage while only children designed their own quiet paradise, leaving middle children to expertly build their chosen families, second-borns to test every boundary, and last-borns to sample life widely—all of which suggests birth order is less a destiny and more a set of starting conditions for how we learn to love, fight, and connect.
Reference
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APA
Lars Eriksen. (2026, February 13). Birth Order Statistics. Gitnux. https://gitnux.org/birth-order-statistics
MLA
Lars Eriksen. "Birth Order Statistics." Gitnux, 13 Feb 2026, https://gitnux.org/birth-order-statistics.
Chicago
Lars Eriksen. 2026. "Birth Order Statistics." Gitnux. https://gitnux.org/birth-order-statistics.
Sources & references
33 datasets cited across this report · attribution is report-level