TABLE 2.

Summary of the excluded studies

Author (reference)	Reason for exclusion
Dillon et al (11), Muraji et al (13), Shimadera et al (17), Foroutan et al (20)	No control group
Escobar et al (16)	Inconsistent steroid protocol
Karrer and Lilly (9), Muraji et al (13), Kobayashi et al (14), Tatekawa et al (15), Stringer et al (19), Shimadera et al (17)*, Lao et al (24)	Did not measure the outcome of interest or did not present sufficient data to calculate RR or OR

^*Shimadera et al published two articles (17,21), both were excluded because they did not have a control group and did not measure the outcome of interest. The study by Muraji et al (13) was excluded to avoid duplication of results because it was a nationwide survey that collected data from other centres in Japan