Table 3.

Total, Natural Direct, and Natural Indirect Effects of Socioeconomic Position at Birth on Frailty Index Score at Age 50 Years^a and Proportion Mediated^b by Socioeconomic Position at Birth^c in the 1958 British Birth Cohort (n = 8,711), 1958–2008^d

	SEP at Birth e , f
Effect	Class III Nonmanual		Class III Manual		Classes IV/V
	Mean %   Difference	95% CI	Mean %   Difference	95% CI	Mean %   Difference	95% CI
Total effect	10.35	3.02, 17.67	27.75	22.23, 33.27	41.96	35.48, 48.44
Natural direct effect (not via adult SEP)	15.28	7.88, 22.69	32.36	26.59, 38.14	23.03	16.36, 29.70
Natural indirect effect (via adult SEP)	−4.94	−7.77, −2.10	−4.61	−7.28, −1.95	18.93	15.49, 22.38
Proportion mediated (via adult SEP)	−0.48	−20.39, 19.43	−0.17	−0.28, −0.06	0.45	0.35, 0.55

Abbreviations: CI, confidence interval; SEP, socioeconomic position.

^a Mean percentage difference in frailty index score.

^b The proportion mediated was the natural indirect effect divided by the total effect.

^c Mediator: adult SEP.

^d The analysis adjusted for sex and for adult physical activity, smoking, and problem alcohol drinking as confounders of the adult SEP–frailty relationship that are themselves influenced by early-life SEP (see text, Figure 1, and Web Appendix 1 for details).

^e SEP at birth was measured as father’s occupational class at birth or, if missing, at age 7 years.

^f Reference group: classes I/II.