Table 1. Regression coefficients for the relationship between age and RBC CR1 level over different age ranges in Kilifi, Kenya.

Age intervals	Regression coefficients	95% CI	P value	N
0–3 Months	−31.24	−64.83–2.35	0.068	73
4–6 Months	−48.08	−62.08–−34.07	<0.001	877
7–12 Months	−6.22	−9.65–−2.79	<0.001	1877
13–24 Months	−4.13	−7.16–−1.09	0.008	547
>2–4 Years	4.25	0.73–7.78	0.018	42
>4–8 Years	−0.33	−2.66–1.99	0.778	62
>8–13 Years	0.94	−1.31–3.19	0.411	57

Abbreviation: CI, confidence interval.

Differences in RBC CR1 levels by age as a continuous variable were analysed by piecewise-linear regression analysis with adjustment for confounding by α⁺thalassaemia and HbS. Age was classified into seven different ranges represented as 0–3 months, 4–6 months, 7–12 months, 1–2 years, >2–4 years, >4–8 years and >8–13 years.