Table 2.

Parameters of development in communication by intellectual disability and Gross Motor Function Classification System (GMFCS) level

	GMFCS level	n	Limit	(95% CI)	50% range around limit	Age90 (y:mo)	(95% CI)	Residual SDs	Offseta
Receptive communication
No intellectual disability	I	194	25.8	(25.7–25.9)	25.8	3:6	(3:4–3:7)	1.1	0.2
	II	42	25.6	(25.3–25.9)	25.1–26.0	3:6	(3:3–3:9)	0.9	0.2
	III	36	25.7	(25.5–26.0)	25.7	3:3	(3:0–3:6)	1.1	0.2
	IV	28	25.8	(25.5–26.0)	25.8	3:5	(3:2–3:9)	1.1	0.2
Intellectual disability	I–IV	72	23.1	(22.1–24.1)	21.0–25.3	4:0	(3:6–4:7)	2.2	0.2
	V	37	16.2	(13.5–18.9)	11.0–21.5	2:6	(1:6–4:4)	3.1	0.2
Expressive communication
No intellectual disability	I	193	61.1	(60.6–61.6)	59.6–62.0	6:1	(5:11–6:3)	2.2	1.0
	II	42	61.0	(59.5–62.4)	59.2–62.0	6:8	(6:2–7:2)	3.7	1.0
	III	36	60.9	(59.3–58.7)	58.7–62.0	6:4	(5:11–6:10)	2.7	1.0
	IV	28	61.1	(59.3–62.5)	58.7–62.0	7:1	(6:7–7:7)	3.3	1.0
Intellectual disability	I–IV	71	40.1	(34.6–45.7)	28.6–51.7	7:0	(5:6–9:0)	5.7	1.0
	V	37	21.7	(14.5–28.9)	7.3–36.1	3:10	(2:6–6:6)	5.3	1.0
Written communication
No intellectual disability	I	166	44.7	(43.6–45.8)	42.3–46.0	16:1	(15:4–16:10)	4.4	5.3
	II	34	41.6	(37.5–45.6)	37.0–46.0	15:9	(14:0–17:11)	4.0	5.3
	III	25	40.9	(35.0–46.7)	35.0–46.0	12:9	(11:4–14:6)	4.3	5.3
	IV	20	37.2	(32.9–41.5)	31.7–42.7	15:0	(13:0–17:6)	3.7	5.3
Intellectual disability	I–IV	38	11.0	(6.3–15.8)	2.5–19.6	17:8	(14:8–21:8)	2.9	5.3
	V	29	4.2	(0.7–7.6)	0.0–9.9	19:2	(15:0–25:2)	2.5	5.3

^aOffset refers to the start age of development in years. CI, confidence interval; SD, standard deviation.