Background In 2009 we presented a method for standardisation of different evidence grading systems (EGS) to simplify the comparison of levels of evidence (LoE) from different guidelines. For this purpose, LoE from guidelines were allocated to a reference standard, the EGS from the Federal Joint Committee’s (G-BA) Code of Procedure. This approach has not yet been tested on several different EGS from guidelines.

Objective To test the feasibility of a method for standardisation of different EGS from COPD, asthma and breast cancer guidelines.

Methods We conducted a systematic search for the above guidelines in guideline databases and websites of guideline providers. The search period covered 11/2007 to 7/2012. Eligible guidelines were evidence-based English or German guidelines using an EGS. The LoE reported were allocated to the EGS from the G-BA’s Code of Procedure.

Results 43 guidelines on chronic diseases with 19 different EGS and 188 different LoE were included. With 4 exceptions, all LoE used in the EGS could be allocated to at least one category of the reference standard. In 44 cases, the LoE from the identified EGS could be allocated to exactly one category and in 63, an LoE was allocated to several categories. Several LoE from one guideline were allocated to one category in 15 cases; this can result in loss of information.

Discussion The testing of a method for standardisation of different EGS indicates that standardisation of LoE using a reference standard can be successfully implemented and can simplify the comparison of different EGS.