Does Birth Spacing Affect Adolescent Cognitive Ability

Among Siblings in Dyads?

AuthorAuthor

Date

Introduction◦ Hypothesis◦ Significance◦ Definitions◦ Pathway

Methods Results Conclusion Q&A

Agenda

Among the population of adolescents in the study, younger siblings of dyad pairs born further apart from their older siblings will have higher cognitive scores than those born closer to their older siblings.

That is, you’ll be smarter if your parents have you and your sibling further in time apart.

Hypothesis

How much time should you plan to set aside to have smart kids?

What makes you smarter than your younger sibling?

Significance

Birth spacing# months between sibling birth dates

Cognitive Ability◦ Peabody Picture Vocabulary Test

Definitions

More attention for child

Different interaction between siblings

More resources for care

Pathway

Mostly infant and early childhood samples

Contradicting results◦ Yes, there is an association1,2,4,5,7,8, 11

◦ No, there is no association3,5, 6, 9, 10, 11

Weak controls in adolescent studies

Literature Review Summary

Study of adolescents

Stronger control for SES, gender, birth order, family size

Different cognitive measure

Our Value Added

Introduction Methods

◦ Study design◦ Exposure & Outcome variables◦ Covariates◦ Models & Interaction

Results Conclusion Q&A

Agenda

Child Health and Development Study Prospective, longitudinal Kaiser Foundation Health Plan, Oakland, California Women and their children born 1959 – 1967 Adolescent Study (born between 1960 – 1963)

Methods: Study Design

Does Birth Spacing Affect Adolescent Cognitive Development? Figure 1.

*also excludes 9 records with inconsistent family size between PREPROD and ADOL

20,754

- Children w/severe anomalies

20,036

- Multiples

19,605

- Children whose mother had hypothyroidism

19,571

- Children not born 1960-1963

9,421

- Children not followed in Adolescent Study

1,900

- Children w/stepsiblings

1,768

- Children w/>1 sibling

384

- Children w/o Peabody score

375

- Children w/older sibling alive at Adol Study* and < 18 yrs older

364

135 Younger siblings

229 35 38 25 37

Older siblings <2 yrs 2-3 yrs 3.1-4 yrs > 4 yrs

Birth space interval = birthday of younger sibling – birthday of older sibling

3 versions of exposure:◦ Categorical exposure◦ Continuous exposure◦ Dual exposure (categorical and continuous)

Methods: Exposure

Version 1: Categorical (5) ◦ Second-born

≤2 years 2.1-3 years 3.1-4 years >4 years

◦ First-born

Version 2: Continuous (months)

Methods: Exposure

Version 3: Dual

◦ Categorical First-born Second-born

◦ Continuous (months)

Methods: Exposure

Continuous Peabody score (points) In general:

◦ SD = 15◦ Range = 0 to 160

In sample:◦ Range = 71 to 156◦ Mean = 117.9◦ SD = 14.3

Methods: Outcome

Methods: Covariates

maternal age race child

sex

sibling sex

delivery type

smoking

child age

head circumfere

nce

social class

marital status

low birthweigh

t

preterm

Methods: Covariates

maternal age race child

sex

sibling sex

delivery type

smoking

child age

head circumfere

nce

social class

marital status

low birthweigh

t

preterm

maternal age race child

sex

sibling sex

Smoking

alcohol

child age

head circumfere

nce

social class

low birthweight

preterm

Methods: Covariates

Significance at p < 0.2

Methods: Covariates

Significance at p < 0.2

maternal age race child

sex

sibling sex

smoking

alcohol

child age

head circumfere

nce

social class

low birthweight

preterm

Methods: Full Model Covariates

Significance: >10% change in coefficient of at least 1 exposure category

maternal age race child

sex

sibling sex

smoking

alcohol

child age

head circumfere

nce

social class

low birthweight

preterm

Methods: Restricted Model Covariates

Significance at > 10% change in coefficient of at least 2 exposure categories

maternal age

race

child sex

smoking

child age

social class

Categorical Birth

spacing

Continuous birth spacing

Dual birth spacing

Full Model 1 Model 2 Model 3

Restricted Model 4 Model 5 Model 6

Interaction,Restricted

Model 7• Model 8• Model 9 • Model 10

N/A

Methods: Linear Regression Models

Continuous birth spacing variable B = 0.001 , p = 0.13

Methods: Quadratic Model Testing

80

100

120

140

pbp

ea

bd

-20 0 20 40 60 80spacemean

bandwidth = .8

Lowess smoother

Tiny magnitude

Pretty linear

Continuous exposure model Significance set at p < 0.2:

1. Birth spacing /race2. Birth spacing /child sex

Revised model Significance set at p < 0.2:

1. Birth spacing /child sex2. Race /child sex3. Birth spacing / child sex / race

Methods: Interaction

Introduction Methods Results

◦ Categorical Model◦ Continuous Model◦ Dual Model◦ Interaction

Conclusion Q&A

Agenda

Characteristic B 95% CI

Birth spacing

Second- born ≤2 yrs -- --

Second- born 2.1-3 yrs -3.1 (-8.9, 2.7)

Second- born 3.1-4 yrs -0.7 (-7.3, 5.8)

Second- born >4 yrs *-9.4 (-15.3, -3.5)

First-born -2.7 (-7.2, 1.9)

Maternal characteristics

Upper class (v. lower) *6.7 (3.9, 9.5)

White (v. other) *7.8 (4.5, 11.2)

Age (years) *0.4 (0.2, 0.7)

Smoking (yes v. no) *-3.9 (-6.7, -1.2)

Child characteristics

Male (v. female) 1.1 (-1.5, 3.8)

Age *4.3 (2.1, 6.5)

* p < 0.05

Results: Categorical Model

Characteristic B 95% CI

Birth spacing (months)

*-0.1 (-0.2, -0.02)

Maternal characteristics

Upper class (v. lower) *2.3 (2.3, 11.4)

White (v. other) 2.9 (-2.2, 9.5)

Age (years) 0.2 (-0.2, 0.7)

Smoking (yes v. no) 2.4 (-8.6, 0.7)

Child characteristics

Male (v. female) 2.2 (-3.7, 5.1)

Age 2.2 (-1.6, 7.0)

* p < 0.05

Results: Continuous Model

Characteristic B 95% CI

Birth spacing (months)

*-0.1 (-0.2, -0.1)

Maternal characteristics

Upper class (v. lower) *6.5 (3.7, 9.2)

White (v. other) *8.0 (4.7, 11.4)

Age (years) *0.5 (0.2, 0.7)

Smoking (yes v. no) *-3.7 (-6.4, -0.9)

Child characteristics

Male (v. female) 1.1 (-1.5, 3.8)

Age *4.5 (2.3, 6.7)

* p < 0.05

Results: Dual Model

Results: InteractionCharacteristic B 95% CI

Intercept β0 *108.3 (100.7, 115.9)

Birth spacing (years) β1 -0.6 (-4.3, 2.8)

Maternal characteristics

Upper class (v. lower) β2 *5.8 (1.3, 10.2)

White (v. other) β3 *9.9 (1.7, 18.1)

Age (years) β4 0.2 (-0.2, 0.6)

Smoking (yes v. no) β5 *-4.0 (-8.6, 0.5)

Child characteristics

Male (v. female) β6 *10.9 (0.9, 20.9)

Age β7 3.0 (-1.2, 7.3)

Interaction

Birth spacing / white β8 0.3 (-3.5, 4.1)

Birth spacing / male β9 *-8.5 (-16.6, -0.4)

White / male β10 *-11.7 (-22.9, -0.48)

Birth spacing/white/male β11 *7.1 (-1.2, 15.5)*p < 0.1

Slope (year) 95% CI Regression equation

White boys -1.8 (-3.3, -0.3)Y = B0 + (B1 + B8 + B9 + B11) yr + B3 + B6 + B10

Other boys -9.2 (-16.5, -1.9)Y = B0 + (B1 + B9) yr + B6

White girls -0.5 (-1.9, 1.0)Y = B0 + (B1 + B8) yr + B3

Other girls -0.8 (-4.3, 2.8)Y = B0 + B1* yr

Results: Interaction

** holding other covariates constant

0.8 1.8 2.8 3.8 4.8 5.8 6.8 7.8 8.80

20

40

60

80

100

120

140

160

Other v. White Boys

Other BoysWhite Boys

Birth spacing (years)

Peab

od

y S

core

Peabody Score by Birth Spacing Interval (years)

0.8 1.8 2.8 3.8 4.8 5.8 6.8 7.8 8.80

20

40

60

80

100

120

140

160Other v. White Girls

Other BoysWhite BoysOther GirlsWhite Girls

Birth spacing (years)

Peab

od

y s

core

Peabody Score by Birth Spacing Interval (years)

Introduction Methods Results Conclusion

◦ Summary◦ Limitations & Strengths◦ Future Directions

Q&A

Agenda

Slight inverse relationship between birth spacing and Peabody score

Negligible difference in Peabody score

Interaction from gender and race

Summary

Small sample size Limited information on first-born siblings

◦ No PREPROD record Unable to compare scores within dyad Operationalizing cognitive ability

Limitations

Statistical rigor◦ Limiting confounders◦ Extensive covariates list◦ Interactions

Strengths

Bigger sample size

Designs that can account for what we could not◦ Different family sizes◦ Intra-family differences in Peabody score◦ Missing covariates

Exploring variables underlying interactions

Future Directions

Introduction Methods Results Conclusion Q&A

◦ Thank you!

Agenda

1. Breland HM. Birth order, family configuration, and verbal achievement, Child Development. 1974;43:1011–1019.

2. Dandes HM and Dow D. Relation of intelligence to family size and density, Child Development. 1969;40: 641–645. 

3. Gibbs ED, Teti DM, Bond LA. Infant-Sibling Communication Relationships to Birth-Spacing and Cognitive and Linguistic Development. Infant Behavior and Development. 1987;10(3):307-324.

4. Kamin KD, Kubinger, Schubert MR. Sibling constellation and intelligence in behavior disordered children, Zeitschrift fur klinische Psychologieforschung und Praxis. 1981;10:98– 109.

5. Lancer I, Rim Y. Intelligence Family Size and Sibling Age Spacing. Personality and Individual Differences. 1984;5(2):151-158.

6. Lewis M, Jaskir J. Infant Intelligence and its Relation to Birth Order and Birth Spacing. Infant Behavior and Development. 1983;6(1):117-120.

7. Nuttall EV and Nuttall RL. Child spacing effects on intelligence, personality, and social competence, Journal of Psychology . 1979;102:3–12.

References

8. Record RG, McKeown T, Edwards HH. An investigation of the difference in measured intelligence between twins and single births, Annals of Human Genetics. 1970;84:11–20.

9. Rodgers JL, Rowe DC. Does Contiguity Breed Similarity? A Within-Family Analysis of Nonshared Sources of IQ Differences between Siblings. Dev Psychol. 1985;21(5):743-

746. 10. Teti DM, Bond LA, Gibbs ED. Sibling-Created Experiences

Relationships to Birth-Spacing and Infant Cognitive Development. Infant Behavior and Development. 1986;9(1):27-42.

11. Wagner ME, Schubert HJP, Schubert DSP. Effects of Sibling Spacing on Intelligence Interfamilial Relations Psychosocial

Characteristics and Mental and Physical Health. Reese, H.W.(Ed.). Advances in Child Development and Behavior, Vol.19.X+260p.Academic Press Inc., Publishers: Orlando, Fla., Usa; Academic Press Inc.(London) Ltd.: London,

England. Illus. 1985:149-206.

References