Table 3.

Publication trend of different study designs

Study design	Publication number	Total citations	Average citations	Average publication year
Survey study	2	514	257	1993
Randomized controlled trial	2	405	203	1994
Quality improvement study	2	301	151	2000
Parallel-design trial	3	809	270	2006
Diagnostic study	10	2883	288	2003
Cross-sectional study	4	1308	327	1984
Comparative effectiveness research	1	171	171	1984
Cohort study	8	2060	258	1998
Case series	5	1382	276	1998