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

Figure 1.
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.

Tables

Table 1. The Strength of Evidence
 
Level of evidenceStudy 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/).
1RCTs
2Cohort studies
3Case-control studies
4Case series/case reports
5Narrative (literature) reviews, editorials

 

Table 2. Research Designs Published in PubMed-Indexed Journals Between 1990 and 2009
 
Study design1990 - 19941995 - 19992000 - 20042005 - 2009P-trend
%/N (95% CI)%/N (95% CI)%/N (95% CI)%/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 trials9.5% (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 trials8.5% (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 studies29.9% (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 studies2.3% (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 reports49.8% (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)
Total58,16370,10186,268118,109

 

Table 3. Research Designs Published in JAMA, NEJM and The Lancet Between 1990 and 2009
 
Study design1990 - 19941995 - 19992000 - 20042005 - 2009P-trend
%/N (95% CI)%/N (95% CI)%/N (95% CI)%/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 trials20.3% (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 trials6.6% (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 studies34.6% (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 studies2.1% (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 reports36.3% (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)
Total538604698562