Table 2.

Association Between Treatment With Azidothymidine and CD4+ T-Lymphocyte Count (cells/mm³) Given 4 Exposure Model Specifications for log₁₀(CD4+), Multicenter AIDS Cohort Study, 1986–1992^a

Variable	Exposure Model Specification
	Linear		Splines		FP		CBPS
	$\stackrel{\mathbf{ˆ}}{\mathbf{\beta }}$	95% CI	$\stackrel{\mathbf{ˆ}}{\mathbf{\beta }}$	95% CI	$\stackrel{\mathbf{ˆ}}{\mathbf{\beta }}$	95% CI	$\stackrel{\mathbf{ˆ}}{\mathbf{\beta }}$	95% CI
Treated at visit 1	−0.10	−0.89, 0.87	−0.25	−0.99, 1.00	−0.23	−0.91, 0.40	−0.21	−0.61, 0.20
Treated at visit 2	0.47	−0.12, 1.16	0.26	−1.02, 1.03	0.24	−0.47, 1.02	0.26	−0.13, 0.65

Abbreviations: AIDS, acquired immunodeficiency syndrome; CBPS, covariate-balancing propensity score; CD4+, CD4-positive; CI, confidence interval; FP, fractional polynomial.

^a 95% CIs were computed by means of the nonparametric bootstrap percentiles approach.