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TRANSCRIPT
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