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Table 2 Evaluation of the studies according to the quality indicators

From: HLA B27 antigen in Middle Eastern and Arab countries: systematic review of the strength of association with axial spondyloarthritis and methodological gaps

Quality Indicator Number of studies / Total studies
Sample size  
 - AS <30 patients 8 / 22
 - AS >50 patients 12 / 22
Presence of control group 11 / 27
Method of HLA-B27 testing stated 3 / 27
Homogeneous and clear inclusion criteria 14 / 22