Flow diagram outlying the selection procedure to identify 183 articles included in the systematic review of biomarkers for disease progression in PD. Note that of the 58 articles identified by reviewing reference lists, 41 were excluded, one article could not be located and 16 were included in the final qualitative synthesis. All eight articles identified by hand searching (all cross-sectional) were included in the final qualitative synthesis.
McGhee et al. BMC Neurology 2013 13:35 doi:10.1186/1471-2377-13-35