Table 2.

Study-level characteristics (N = 53).

Country and design			Child characteristics			Adult characteristics
Country	Study count	%	Child sample size	Study count	%	Mean education	Study count	%
United States	45	84.9	21–40	19	35.8	> high school	34	64.2
Canada	3	5.7	0–20	18	34.0	Not reported	15	28.3
England	1	1.9	81–100	4	7.5	< or = high school	4	7.5
China	2	3.8	> 301	4	7.5	Mean age
Korea	1	1.9	201–300	3	5.7	Not reported	47	88.7
Not reported	1	1.9	41–60	2	3.8	30–40	3	5.7
Design			61–80	2	3.8	< 30	1	1.9
RCT/quasi	4	7.5	100–200	1	1.9	41–50	1	1.9
Natural expmt	1	1.9	Mean child age a			70–80	1	1.9
Single case	3	5.7	Toddler	35	34.3	% minority
Descriptive	36	67.9	Preschool	32	31.4	Not reported	37	69.8
Psychometric	9	17.0	Infant	25	24.5	0–24	14	26.4
Languages a			Kindergarten	6	5.9	50–74	1	1.9
English	49	75.4	Early elementary	3	2.9	75–100	1	1.9
Spanish	11	16.9	Not reported	1	1.0	25–49	0	0.0
Chinese	2	3.1	% male
French	1	1.5	0–49	23	43.4
Korean	1	1.5	50–100	21	39.6
German	1	1.5	Not reported	9	17.0
			SES
			Not low SES	47	88.8
			Low SES	6	12.2
			Disability a
			TD	28	52.8
			Deaf/HI	12	22.6
			ASD/PDD	10	18.9
			SPLD	7	13.2
			Other	7	13.2
			Not reported	2	3.8

Note. RCT = randomized control trial; quasi = quasi-experimental design; expmt = experiment; SES = socioeconomic status; TD = typically developing; HI = hearing impaired; ASD = autism spectrum disorder; PPD = pervasive development disorder; SPLD = speech and language delay.

^a Where values summed greater than 53, variables occurred multiple times in studies.