Table 3.

Results from two LRR models for weight among infants exposed to HIV infection. The parametric model estimated the reference time trend using natural cubic spline bases with knots at 150, 500, and 1100 days. The semi-parametric model estimated the reference time trend using a penalized spline equation with knots at day 1, 1 week, 6 weeks, 10 weeks, 15 weeks, 6 months, 1 year, and every half year there after (17 knots in total). Both models provide estimates for main effects, rate effects for sex, treatment, and HIV infection status. The rate structure included an interaction between the three covariates and an indicator for observations measured after 2 years from birth. The rate effects for each model can be interpreted as the difference in the rate of change associated with a given covariate prior to 2 years. The rate interaction effects estimate the change in the rate effect after 2 years. Estimates of the coefficients for the time trend of each model are omitted in the table.

	Parametric Model		Semi-Parametric Model
	Estimate	95% CI	Estimate	95% CI
Baseline Effects
Intercept	3.33	(3.25, 3.42)	3.10	(3.01, 3.19)
Sex (Male)	0.18	(0.08, 0.27)	0.16	(0.07, 0.26)
Treatment (Nev)	−0.14	(−0.23, −0.05)	−0.14	(−0.23, −0.04)
HIV Status	−0.02	(−0.13, 0.10)	−0.07	(−0.23, 0.09)
Rate Effects
Sex (Male)	0.05	(0.02, 0.08)	0.05	(0.02, 0.08)
Treatment (Nev)	0.01	(−0.02, 0.04)	0.01	(−0.02, 0.04)
HIV Status	−0.12	(−0.17, −0.07)	−0.12	(−0.18, −0.07)
Rate Interaction (After 2 years)
Sex (Male)	−0.07	(−0.10, −0.04)	−0.07	(−0.09, −0.04)
Treatment (Nev)	−0.01	(−0.04, 0.01)	0.00	(−0.03, 0.02)
HIV Status	−0.11	(−0.17, −0.05)	−0.12	(−0.17, −0.06)