Seventeen studies (n=3,713) were included: 14 randomised controlled trials (RCTs; n=3,661), one prospective double-blind matched study (n=16), one quasi-experimental study (n=26) and one prospective triple-blind study (n=10). The sample size ranged from 10 to 1,691; the sample size was less than 50 in 10 studies.
One of the 14 RCTs was triple-blind, twelve were double-blind and one was retroactive.
Ten studies (including 8 RCTs) reported no significant differences in outcomes between intercessory prayer and control groups.
Seven studies (including 6 RCTs) reported significant improvements in some outcomes in patients receiving intercessory prayer compared with control.
The meta-analysis showed small significant beneficial effects for intercessory prayer compared with control when using both random-effects and fixed-effect models: ES -0.171 (p=0.015) and ES -0.095 (p=0.006), respectively.