Background: Language restriction can be a problem for collecting the
relevant research data when we conduct systematic reviews. Some
Japanese written journals are covered in MEDLINE or other international
medical literature databases, but some are covered by Japanese databases
only. Data from relevant randomized controlled trials (RCTs) in Japan may
be lost due to language restriction, if the review team does not have
access to Japanese database. Objectives: To assess the number of
reporting of RCTs in Japanese database compared with MEDLINE reporting
Japanese literature numbers. Methods: We conducted a comprehensive
search using the term ‘randomized controlled trial’ in MEDLINE from 1980
to 2008, and in the Japanese electronic databases Japana Centra Revuo
Medicina (ICHUSHI) and Webcat Plus, CiNii, J-Stage, and Medical Online.
Results: From 1999 to 2007, 3162 RCTs were reported in ICHUSHI. Before
1999, the term of RCTs had not been used in ICHUSHI database as an
indexing term. Recently, more than 500 RCTs were reported in ICHUSHI
every year. In 2006, 662 RCTs were reported in ICHISHI, while 48% were
listed in MEDLINE, but the rest of RCTs were not covered by MEDLINE. The
area of RCTs reported in ICHUSHI were cardiology 22%, orthopedics 16%,
gastroenterology 8%, respectively. RCTs reported only in ICHUSHI and not
in MEDLINE were orthopedics 28% and cardiology 17%, respectively.
Conclusions: The number of RCTs published in Japanese was substantial.
The Japanese RCTs were also becoming valuable resources of systematic
reviews. The access to the Japanese medical literature databases may help
for collecting the relevant researches when you conduct systematic
reviews. Local language literature databases may not be neglected to
collect the updated study results.