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

Table 2 Evaluation of the studies according to the quality indicators

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

ISSN: 1471-2474