 A number of people have tried to conduct statistical studies to determine whether or not petitionary prayer is effective. These studies try to measure the differences between groups of people, one of which is the subject of petitionary prayers, and the other of which is not. Although some earlier studies suggested a positive correlation between patient recovery and petitionary prayer (see Byrd 1998; Harris, et al. 1999; and Leibovici 2001), more recent studies have suggested that the offering of petitionary prayer (and the knowledge that such prayers were offered) is not positively correlated with patient recovery (see Benson et al. 2006).