J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website http://www.jocmr.org

Original Article

Volume 7, Number 6, June 2015, pages 428-434

Clinical Research Quo Vadis? Trends in Reporting of Clinical Trials and Observational Study Designs Over Two Decades

Figure 1. New reports on human subjects research by design and per year. (a) All Journals indexed in PubMed. (b) The New England Journal of Medicine. (c) The Journal of the American Medical Association. (d) The Lancet. The absolute number of human subjects research reports published per year is graphed for the time period between 1990 and 2009 and per study design, respectively. The number of reports publised increased for all study designs considered.

**Table 1.** The Strength of Evidence
Level of evidence	Study design
This table outlines the traditional hierarchy of study designs and evidence levels. The table is simplified and contains major categories of study designs only. Adopted from the Oxford Centre for Evidence-based Medicine (http://www.cebm.net/).
1	RCTs
2	Cohort studies
3	Case-control studies
4	Case series/case reports
5	Narrative (literature) reviews, editorials

Table 1. The Strength of Evidence

Level of evidence

Study design

This table outlines the traditional hierarchy of study designs and evidence levels. The table is simplified and contains major categories of study designs only. Adopted from the Oxford Centre for Evidence-based Medicine (http://www.cebm.net/).

RCTs

Cohort studies

Case-control studies

Case series/case reports

Narrative (literature) reviews, editorials

**Table 2.** Research Designs Published in PubMed-Indexed Journals Between 1990 and 2009
Study design	1990 - 1994	1995 - 1999	2000 - 2004	2005 - 2009	P-trend
Numbers are counts and averaged proportions per year for each time period. r is correlation coefficient for study design frequency and year of publication. P-value is for time trend between 1990 and 2009.
Randomized clinical trials	9.5% (8.8 - 10.3) 5,679 (4,810 - 6,548)	10.1% (9.8 - 10.4) 7,099 (6,561 - 7,638)	10.1% (9.7 - 10.5) 8,984 (7,290 - 10,678)	10.3% (10.1 - 10.5) 12,140 (10,699 - 13,580)	0.052 (r = 0.57)
Clinical trials	8.5% (5.0 - 12.1) 5,020 (2,042 - 7,999)	11.8% (11.4 - 12.3) 8,312 (7,437 - 9,188)	10.7% (9.8 - 11.5) 9,217 (7,441 - 10,993)	9.6% (8.3 - 11.0) 11,323 (9,879 - 12,766)	0.99 (r = 0.06)
Cohort and case-control studies	29.9% (27.4 - 32.4) 17,330 (15,076 - 19,583)	24.5% (33.5 - 35.4) 24,193 (22,014 - 26,371)	37.8% (36.7 - 38.8) 32,526 (27,513 - 37,539)	40.5% (39.4 - 41.6) 47,871 (42,804 - 52,938)	< 0.001 (r = 0.97)
Cross-sectional studies	2.3% (1.9 - 2.6) 1,313 (982 - 1,644)	2.9% (2.6 - 3.1) 2,021 (1,707 - 2,335)	3.9% (3.5 - 4.4) 3,430 (2,536 - 4,324)	6.0% (5.3 - 6.8) 7,146 (5,548 - 8,745)	< 0.001 (r = 0.96)
Case reports	49.8% (47.0 - 52.6) 28,821 (27,745 - 29,897)	40.7% (39.4 - 41.9) 28,476 (27,670 - 29,281)	37.5% (35.6 - 39.5) 32,111 (30,452 - 33,770)	33.6% (32.9 - 34.2) 39,629 (36,652 - 42,605)	< 0.001 (r = -0.95)
Total	58,163	70,101	86,268	118,109

Table 2. Research Designs Published in PubMed-Indexed Journals Between 1990 and 2009

Study design

1990 - 1994

1995 - 1999

2000 - 2004

2005 - 2009

P-trend

%/N (95% CI)

Numbers are counts and averaged proportions per year for each time period. r is correlation coefficient for study design frequency and year of publication. P-value is for time trend between 1990 and 2009.

Randomized clinical trials

9.5% (8.8 - 10.3)
5,679 (4,810 - 6,548)

10.1% (9.8 - 10.4)
7,099 (6,561 - 7,638)

10.1% (9.7 - 10.5)
8,984 (7,290 - 10,678)

10.3% (10.1 - 10.5)
12,140 (10,699 - 13,580)

0.052 (r = 0.57)

Clinical trials

8.5% (5.0 - 12.1)
5,020 (2,042 - 7,999)

11.8% (11.4 - 12.3)
8,312 (7,437 - 9,188)

10.7% (9.8 - 11.5)
9,217 (7,441 - 10,993)

9.6% (8.3 - 11.0)
11,323 (9,879 - 12,766)

0.99 (r = 0.06)

Cohort and case-control studies

29.9% (27.4 - 32.4)
17,330 (15,076 - 19,583)

24.5% (33.5 - 35.4)
24,193 (22,014 - 26,371)

37.8% (36.7 - 38.8)
32,526 (27,513 - 37,539)

40.5% (39.4 - 41.6)
47,871 (42,804 - 52,938)

< 0.001 (r = 0.97)

Cross-sectional studies

2.3% (1.9 - 2.6)
1,313 (982 - 1,644)

2.9% (2.6 - 3.1)
2,021 (1,707 - 2,335)

3.9% (3.5 - 4.4)
3,430 (2,536 - 4,324)

6.0% (5.3 - 6.8)
7,146 (5,548 - 8,745)

< 0.001 (r = 0.96)

Case reports

49.8% (47.0 - 52.6)
28,821 (27,745 - 29,897)

40.7% (39.4 - 41.9)
28,476 (27,670 - 29,281)

37.5% (35.6 - 39.5)
32,111 (30,452 - 33,770)

33.6% (32.9 - 34.2)
39,629 (36,652 - 42,605)

< 0.001 (r = -0.95)

Total

58,163

70,101

86,268

118,109

**Table 3.** Research Designs Published in JAMA, NEJM and The Lancet Between 1990 and 2009
Study design	1990 - 1994	1995 - 1999	2000 - 2004	2005 - 2009	P-trend
Numbers are counts and averaged proportions per year for each time period. r is correlation coefficient for study design frequency and year of publication. P-value is for time trend between 1990 and 2009.
Randomized clinical trials	20.3% (18.5 - 22.0) 109 (95 - 123)	22.5% (19.8 - 25.3) 137 (109 - 164)	25.9% (24.3 - 27.5) 180 (174 - 187)	30.9% (29.8 - 31.9) 174 (166 - 182)	< 0.001 (r = 0.91)
Clinical trials	6.6% (4.9 - 8.3) 36 (24 - 47)	4.5% (3.8 - 5.2) 27 (23 - 32)	3.8% (3.1 - 4.5) 26 (22 - 31)	3.7% (3.2 - 4.2) 21 (17 - 25)	0.001 (r = -0.74)
Cohort and case-control studies	34.6% (33.4 - 35.8) 186 (173 - 199)	32.1% (30.6 - 33.6) 194 (175 - 213)	26.4% (23.2 - 29.5) 185 (146 - 224)	19.2% (16.5 - 21.9) 108 (84 - 132)	< 0.001 (r = -0.94)
Cross-sectional studies	2.1% (1.5 - 2.8) 12 (7 - 16)	4.1% (3.4 - 4.8) 25 (18 - 32)	3.1% (2.2 - 3.9) 21 (13 - 29)	2.4% (1.7 - 3.1) 13 (8 - 19)	0.99 (r = 0.01)
Case reports	36.3% (35.2 - 37.5) 195 (182 - 209)	36.7% (33.8 - 39.5) 221 (202 - 240)	40.8% (37.2 - 44.4) 286 (238 - 333)	43.8% (41.5 - 46.1) 246 (229 - 262)	< 0.001 (r = 0.77)
Total	538	604	698	562

Table 3. Research Designs Published in JAMA, NEJM and The Lancet Between 1990 and 2009

Study design

1990 - 1994

1995 - 1999

2000 - 2004

2005 - 2009

P-trend

%/N (95% CI)

Randomized clinical trials

20.3% (18.5 - 22.0)
109 (95 - 123)

22.5% (19.8 - 25.3)
137 (109 - 164)

25.9% (24.3 - 27.5)
180 (174 - 187)

30.9% (29.8 - 31.9)
174 (166 - 182)

< 0.001 (r = 0.91)

Clinical trials

6.6% (4.9 - 8.3)
36 (24 - 47)

4.5% (3.8 - 5.2)
27 (23 - 32)

3.8% (3.1 - 4.5)
26 (22 - 31)

3.7% (3.2 - 4.2)
21 (17 - 25)

0.001 (r = -0.74)

Cohort and case-control studies

34.6% (33.4 - 35.8)
186 (173 - 199)

32.1% (30.6 - 33.6)
194 (175 - 213)

26.4% (23.2 - 29.5)
185 (146 - 224)

19.2% (16.5 - 21.9)
108 (84 - 132)

< 0.001 (r = -0.94)

Cross-sectional studies

2.1% (1.5 - 2.8)
12 (7 - 16)

4.1% (3.4 - 4.8)
25 (18 - 32)

3.1% (2.2 - 3.9)
21 (13 - 29)

2.4% (1.7 - 3.1)
13 (8 - 19)

0.99 (r = 0.01)

Case reports

36.3% (35.2 - 37.5)
195 (182 - 209)

36.7% (33.8 - 39.5)
221 (202 - 240)

40.8% (37.2 - 44.4)
286 (238 - 333)

43.8% (41.5 - 46.1)
246 (229 - 262)

< 0.001 (r = 0.77)

Total

538

604

698

562