Does Birth Spacing Affect Adolescent Cognitive Ability Among Siblings in Dyads?

1. Does Birth Spacing Affect Adolescent Cognitive Ability Among Siblings in Dyads? Author Author Date

2. Agenda • Introduction • Hypothesis • Significance • Definitions • Pathway • Methods • Results • Conclusion • Q&A

3. Hypothesis • 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.

4. Significance • How much time should you plan to set aside to have smart kids? • What makes you smarter than your younger sibling?

5. Definitions • Birth spacing # months between sibling birth dates • Cognitive Ability • Peabody Picture Vocabulary Test

6. Pathway • More attention for child • Different interaction between siblings • More resources for care

7. Literature Review Summary • 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

8. Our Value Added • Study of adolescents • Stronger control for SES, gender, birth order, family size • Different cognitive measure

9. Agenda • Introduction • Methods • Study design • Exposure & Outcome variables • Covariates • Models & Interaction • Results • Conclusion • Q&A

10. Methods: Study Design • 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)

11. Does Birth Spacing Affect Adolescent Cognitive Development? Figure 1. *also excludes 9 records with inconsistent family size between PREPROD and ADOL

12. Methods: Exposure • Birth space interval = birthday of younger sibling – birthday of older sibling • 3 versions of exposure: • Categorical exposure • Continuous exposure • Dual exposure (categorical and continuous)

13. 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)

14. Methods: Exposure • Version 3: Dual • Categorical • First-born • Second-born • Continuous (months)

15. Methods: Outcome • Continuous Peabody score (points) • In general: • SD = 15 • Range = 0 to 160 • In sample: • Range = 71 to 156 • Mean = 117.9 • SD = 14.3

16. Methods: Covariates

17. Methods: Covariates

18. Methods: Covariates Significance at p < 0.2

19. Methods: Covariates Significance at p < 0.2

20. Methods: Full Model Covariates Significance: >10% change in coefficient of at least 1 exposure category

21. Methods: Restricted Model Covariates Significance at > 10% change in coefficient of at least 2 exposure categories

22. Methods: Linear Regression Models

23. Methods: Quadratic Model Testing Tiny magnitude • Continuous birth spacing variable • B = 0.001 , p = 0.13 Pretty linear

24. Methods: Interaction Continuous exposure model • Significance set at p < 0.2: • Birth spacing /race • Birth spacing /child sex Revised model • Significance set at p < 0.2: • Birth spacing /child sex • Race /child sex • Birth spacing / child sex / race

25. Agenda • Introduction • Methods • Results • Categorical Model • Continuous Model • Dual Model • Interaction • Conclusion • Q&A

26. Results: Categorical Model

27. Results: Continuous Model

28. Results: Dual Model

29. Results: Interaction

30. Results: Interaction ** holding other covariates constant

31. Peabody Score by Birth Spacing Interval (years)

32. Peabody Score by Birth Spacing Interval (years)

33. Agenda • Introduction • Methods • Results • Conclusion • Summary • Limitations & Strengths • Future Directions • Q&A

34. Summary • Slight inverse relationship between birth spacing and Peabody score • Negligible difference in Peabody score • Interaction from gender and race

35. Limitations • Small sample size • Limited information on first-born siblings • No PREPROD record • Unable to compare scores within dyad • Operationalizing cognitive ability

36. Strengths • Statistical rigor • Limiting confounders • Extensive covariates list • Interactions

37. Future Directions • 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

38. Agenda • Introduction • Methods • Results • Conclusion • Q&A • Thank you!

39. References • Breland HM. Birth order, family configuration, and verbal achievement, Child Development. 1974;43:1011–1019. • Dandes HM and Dow D. Relation of intelligence to family size and density, Child Development. 1969;40: 641–645.  • 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. • Kamin KD, Kubinger, Schubert MR. Sibling constellation and intelligence in behavior disordered children, Zeitschrift fur klinischePsychologieforschung und Praxis. 1981;10:98– 109. • Lancer I, Rim Y. Intelligence Family Size and Sibling Age Spacing. Personality and Individual Differences. 1984;5(2):151-158. • Lewis M, Jaskir J. Infant Intelligence and its Relation to Birth Order and Birth Spacing. Infant Behavior and Development. 1983;6(1):117-120. • Nuttall EV and Nuttall RL. Child spacing effects on intelligence, personality, and social competence, Journal of Psychology . 1979;102:3–12.

40. References • 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. • 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. • 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. • 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.