TABLE 2.

Summary of characteristics of experimental and quasi-experimental group-comparison studies, 1940–2014^a

Study Characteristics	1940s, k =1	1950s, k = 4	1960s, k = 6	1970s, k = 7	1980s, k = 23	1990s, k = 21	2000s, k = 24	2010–2014, k = 30
Average sample size	80	106	57	37	39	44	123	382
Total hours of intervention, %
≤5	0	0	17	14	39	43	4	3
6–15	100	0	33	29	30	24	21	27
16–25	0	0	17	0	0	5	29	10
>25	0	75	33	29	0	19	42	60
Not reported	0	25	0	29	30	10	4	0
Intervention typeb, %
Vocabulary	0	0	0	0	30	5	0	10
Comprehension strategy	0	0	0	0	39	57	33	20
Fluency	0	0	0	0	9	10	13	7
Multicomponent	100	75	17	0	22	14	42	63
Word study	0	0	0	57	0	14	13	0
Multisensoryc	100	0	17	57	0	14	4	0
Visual trainingc	100	0	17	29	0	14	0	0
Psychiatric/behavior/emotional treatmentc	0	50	17	0	0	0	0	3
Other	0	25	83	43	0	0	0	0
Types of comparison group, %
No treatment	0	50	33	29	9	19	4	3
Business as usual	0	25	0	29	9	24	58	80
Attention control	0	0	17	0	17	5	4	7
Absence of selected component	0	25	17	14	17	19	13	3
Different treatment	100	0	33	29	48	33	21	7
Types of outcome measures, %
Standardized	0	50	67	29	4	19	46	50
Unstandardized	0	25	0	14	78	62	21	17
Both	0	25	33	43	17	19	33	3
Unclear	100	0	0	14	0	0	0	0
Grades, %
4–8	100	75	67	86	78	81	92	70
9–12	0	25	17	0	22	19	8	20
Other/not clear	0	0	17	14	0	0	0	10
LD status, %
All LD	0	25	0	0	83	57	29	7
Some LD	0	0	0	0	9	19	33	30
No LD	0	0	0	0	0	5	13	10
Other/not clear	100	75	100	100	9	19	25	53

Note. LD = learning disability.

^aNo studies published before 1940 used a group comparison experimental or quasi-experimental design.

^bSome studies contrasted more than one intervention type, leading to totals in excess of 100% for some decades.

^cIn addition to a reading intervention.