Subgroup Characteristics Number of studies Pooled RR(95%CI) Z-value P-value
Study design
Prospective studies 2 0.531(0.348-0.812) 2.93 0.003
Retrospective studies 7 0.746(0.613-0.907) 2.94 0.003
A history of stroke
Patients with and without stroke 8 0.726(0.591-0.893) 3.04 0.000
Patients with stroke only 1 0.650(0.580-0.720) 7.81 0.002
Observational window
Yes 4 0.745(0.505-1.100) 1.48 0.138
No 5 0.720(0.612-0.848) 3.94 0.000