Preventable Adverse Drug Reactions – Meta-Analysis Figure 3. Percentage of patients with preventable adverse drug reactions among outpatients being hospitalised or visiting emergency care. *not provided directly in the study, interpreted from other presented data. doi:10.1371/journal.pone.0033236.g003 [30,43,44,46], and three included the whole hospital [23,41,42]. All studies included adults of all ages. In six studies [23,30,43-46], preventability was assessed by the consensus of at least two professionals, and the number of assessors was unclear in two [41,42]. All studies [23,30,41-45], except for one [46], used either Hallas [39] or Schumock [40] criteria for determining prevent- ability. Preventable adverse drug reactions among outpatients The 16 studies on outpatients involved 48797 emergency visits or hospital admissions. PADRs occurred in 2% (95% confidence interval (CI): 1.2–3.2%) of outpatients (Figure 3), and 52% (95% CI: 42–62%) of ADRs present at the time of hospitalisation or an emergency visit were preventable (Figure 4). The preventability was higher in the three studies including only the elderly, for which 71% (95% CI: 51–91%) of ADRs were preventable. Preventable adverse drug reactions among inpatients In total 24128 inpatients were included in the eight studies on ADRs present during hospital stay. In inpatients, 1.6% (95% CI: 0.1–51%) experienced a PADR during hospital stay (Figure 5). Among inpatients, we found that 45% (95% CI: 33–58%) of ADRs were assessed as preventable (Figure 6). Figure 4. Preventability of adverse drug reactions among outpatients being hospitalised or visiting emergency care. *not provided directly in the study, interpreted from other presented data. doi:10.1371/journal.pone.0033236.g004 PLoS ONE | www.plosone.org 6 March 2012 | Volume 7 | Issue 3 | e33236