Did the JFK assassination affect the secondary sex ratio?

1. Did the JFK assassination affect the secondary sex ratio? Author 1 Author 2

2. Secondary Sex Ratio (SSR) • Odds or proportion of male live births: Male births Female births Male births Male + female births or • Typically 1.05-1.07

3. Variations in SSR • Community stressors • War • Economic collapse • Natural disasters • Terrorism • Maternal factors • Smoking • Age • Environmental toxins

4. Unanswered Questions • Sudden community stressor (assassination of a sitting president) • No mass casualties • Fetal death vs. conception theories

5. Public Health Relevance • How community stressors affect biological outcomes and maternal health • Marker of population stress • Measure of prospective population fertility

6. Subjects

7. Model 1 ref group: Pre-assassination births (3 months) Model 2 ref group: Pre-assassination births (full sample) Model 3 ref group: Pre-assassination births (seasonal) Births of women exposed in 3rd trimester Exposure: JFK assassination Model 4 ref group: Pre-assassination births (seasonal) Births of women exposed in 2nd trimester Model 5 ref group: Pre-assassination births (seasonal) Births of women exposed in 1st trimester Model 6 ref group: Pre-assassination births (seasonal) Births of women exposed in 3 months post-assassination November 1963 November 1959 November 1960 November 1961 November 1962 Figure 2: Timeline of births by exposure to JFK assassination during pregnancy and categorization in multivariate models, Child Health and Development Studies, 1959-1967

8. Statistical Analysis • Multiple logistic regression • 7 models • Variations in unexposed comparison group (2) • Controlling for seasonal patterns (4) • Assessing interaction (1) • Null hypothesis: The JFK assassination was not associated with a change in the SSR.

9. Statistical Analysis • Selection of covariates • No assessment of confounding in community stressor literature • Univariate and bivariate analyses of individual characteristics associated with SSR (chi-square tests) • Husband’s age • Maternal age • Parental age gap • Maternal BMI • Marital status • Maternal race • Maternal smoking • Husband’s smoking

10. Results: Descriptive

11. Results: Main Effects • SSR in 3-month unexposed group: 1.17 • SSR in full unexposed group: 1.06 • SSR lower in cohort exposed in 2nd trimester: 0.81 • Results presented as odds of male birth compared to reference groups

12. Results: Model 1Main effects, 3-month unexposed group

13. Results: Model 2Main effects, full unexposed group

14. Results: Models 3-6Main effects, exploring seasonal variation

15. Results: Confounding and Interaction • Chi-square tests identified no possible confounders • Based on literature, tested for interaction using Model 2 sample: • Maternal smoking (binary) • Husband’s smoking (binary) • Maternal age (continuous) • Significant likelihood-ratio tests for husband’s smoking interaction terms in trimesters 2 and 3

16. Results: Model 7Inclusion of interaction terms

17. Results: Model 3Seasonal model, inclusion of interaction terms

18. Results: Model 4Seasonal model, inclusion of interaction terms

19. Conclusions • JFK assassination associated with lower SSR in women exposed in 2nd trimester, accounting for seasonal variations in SSR • Community stressors without mass casualties can affect population fertility • Supports fetal death hypothesis

20. Discussion • Interaction with husband’s smoking • Lower SSR in trimester 2 when husbands smoked • Higher SSR in trimester 3 when husbands smoked • Fukuda et al. found lower SSR when fathers smoked heavily • No evidence in literature of link between smoking and higher SSR • May be anomaly resulting from missing data

21. Limitations • Variation in gestation length may have resulted in misclassification • Need large sample size to detect SSR effects • Missing data in husband’s smoking variable (31%)

22. Future Directions • Repeat analysis using time-series methods • Repeat analysis with larger cohort if data are available • Examine rate of fetal death in women exposed during 2nd trimester