Table 2.

Descriptive Statistics for the Offline Vocabulary and Grammar Measures From the CDI and PPVT–R

Age	Words understooda		Words producedb		Grammatical complexityc		M3Ld		PPVT–Re
	M	SD	M	SD	M	SD	M	SD	M	SD
12 months	82.5	62.3	9.6	10.8	—		—		—
15 months	166.2	88.7	28.9	30.7	—		—		—
18 months	—		95.6	101.4	1.1	4.4	1.8	1.0	—
21 months	—		208.5	158.9	5.2	7.4	3.1	1.7	—
25 months	—		391.7	176.8	13.5	11.5	5.5	3.1	13.7	5.4

Note. CDI = MacArthur–Bates Communicative Development Inventory; PPVT–R = Peabody Picture Vocabulary Test—Revised; M3L = mean of the three longest utterances; dash = data are not available.

^aNumber of words reported as “understands” on the CDI: Words and Gestures (reported at 12 and 15 months).

^bNumber of words reported as “understands and says” on the CDI: Words and Gestures (reported at 12 and 15 months) or CDI: Words and Sentences (reported at 18, 21, and 25 months).

^cNumber of times the parent chose the second (more complex) example on the complexity section of the CDI: Words and Sentences (reported at 18, 21, and 25 months).

^dM3L reported on the CDI: Words and Sentences (reported at 18, 21, and 25 months).

^eCeiling score minus errors from the PPVT–R, administered at 25 months.