Table 3.

Incidence Rate Ratios, Stratified by Age Group at Baseline, for the Effect of Body Mass Index on Mortality in Postmenopausal Women in the Women’s Health Initiative Clinical Trials, United States, 1993–2005

Age Group and BMIa	Adjusted, Unweighted Resultsb		IPTW × IPCW Weighted Marginal Structural Modelc
	IRR	95% CI	IRR	95% CI
50–59 years
<18.5	5.17	2.07, 8.28	5.97	3.27, 10.91
18.5–24.9	1.44	1.08, 1.81	1.52	1.18, 1.97
25.0–29.9	1.0	Referent	1.0	Referent
30.0–34.9	0.96	0.71, 1.21	1.05	0.80, 1.37
35.0–39.9	1.17	0.84, 1.52	1.53	1.13, 2.06
≥40.0	0.91	0.59, 1.24	1.43	1.00, 2.05
60–69 years
<18.5	3.42	1.91, 4.93	2.83	1.80, 4.44
18.5–24.9	1.53	1.30, 1.76	1.44	1.24, 1.68
25.0–29.9	1.0	Referent	1.0	Referent
30.0–34.9	0.85	0.71, 0.99	0.96	0.82, 1.14
35.0–39.9	0.88	0.71, 1.07	1.03	0.83, 1.26
≥40.0	0.80	0.58, 1.02	1.11	0.85, 1.46
70–79 years
<18.5	4.80	2.92, 6.67	3.46	2.29, 5.22
18.5–24.9	1.41	1.17, 1.65	1.29	1.10, 1.51
25.0–29.9	1.0	Referent	1.0	Referent
30.0–34.9	0.83	0.66, 1.00	0.86	0.73, 1.07
35.0–39.9	0.59	0.40, 0.77	0.84	0.62, 1.12
≥40.0	1.27	0.78, 1.77	1.35	0.89, 2.05

Abbreviations: CI, confidence interval; BMI, body mass index; IPCW, inverse probability of censoring weights; IPTW, inverse probability of treatment weights; IRR, incidence rate ratio.

^a Weight (kg)/ height (m)².

^b The unweighted model adjusted for baseline covariates plus time-varying confounders (age, trial arm, race/ethnicity, education, marital status, income, health insurance status, smoking status and history, disease status (cardiovascular disease, cancer, fracture), hormone therapy use, self-rated health, physical activity level, alcohol intake, physical functioning, hypertension, and diabetes).

^c Adjusted only for baseline covariates (age, trial participation and assignment arm, race/ethnicity, education, marital status, income, health insurance status, and smoking status and history).