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 database, but some are covered by Japanese database only. Data from relevant randomized controlled trials in Japan may be lost due to language restriction, if the review team does not have the access to Japanese database.
Objectives: To assess the number of reporting of randomized controlled trials in Japanese database comparing Medline reporting Japanese literature number.
Methods: We conducted a comprehensive search using the term of ‘randomized controlled trial’, including Medline from 1983 to 2011, and Japanese electronic databases Japana Centra Revuo Medicina (ICHUSHI).
Results: RCTs published in Japanese-based journal have been incorporated in Medline since 1987. When we compared RCTs published in Japanese-based journal in Medline with those in ICHUSHI, Medline incorporated approximately same number of RCTs in Japanese-based journals incorporated in ICHUSHI in 1995. After 2000, number of RCTs published in Japanese-based journal but not incorporated in Medline has increased dramatically. In 2011, 627 articles were classified as RCTs in ICHUSHI. Our survey revealed only 382 articles (52.3%) were true RCTs, and others were not RCTs.
Conclusions: The number of RCTs published in Japanese-based journal increases year by year. The Japanese RCTs were also becoming valuable resources of systematic reviews. Some of Japanese RCTs are not incorporated in Medline. The access to the Japanese Medical literature database may help for collecting the relevant researches to conduct systematic reviews. Local language literature database may not be neglected to collect the updated study result.