Preventable Adverse Drug Reactions – Meta-Analysis Table 2. Characteristics of included studies on preventable adverse drug reactions among outpatients visiting emergency care. Study (Country) Patel 2007 [32] (India) Zed 2008 [38] (Canada) Tafreshi 1999 [26] (United States) Study period 6 weeks, 2005 12 weeks, 2006 35 days, 1996 Study design Prospective, observational Prospective, observational Prospective, observational Population characteristics Age.18 years Characteristics of patients with ADR Mean age 40 years. Definition for ADR{ WHO [16] Criteria for preventability Modified Hallas [39] Mean age 50 years, 48% male Mean age 53 years (range 0, 1–95), 43% male Unknown Unknown Similar to WHO [16] Hallas [39] Similar to WHO [16] Own criteria ADR = adverse drug reaction; WHO = World Health Organization. {Studies using WHO’s definition may have referenced another publication for the definition. doi:10.1371/journal.pone.0033236.t002 Study characteristics Sixteen included studies reported PADRs among outpatients being hospitalised or visiting emergency care (Tables 1,2) [23-38]. We did not identify any studies in primary care without a hospitalisation or emergency visit. Nine studies were conducted in Europe [28-31,33-37], two in Australia [25,27], four in North America [23,24,26,38], and one India [32]. The studies were conducted between 1992 and 2006. The study periods ranged from two weeks [35] to 21 months [36]. Fourteen studies had a prospective design [23-26,28-36,38], one retrospective [37], and one cross-sectional [27]. All 16 studies used medical records as the source of information, combined to reporting of ADRs or interviewing patients or their family. Of these, 11 studies were conducted in some wards [24-30,32-34,38], four included the whole hospital [23,31,35,36], and one used a population database of general practitioners as a source of recruitment [37]. Three studies were conducted exclusively in the elderly ($65 years) [24,27,34]. Except for two studies [24,32], all assessed the preventability by the consensus of at least two professionals [23,25-31,33-38]. For determining preventability, the criteria introduced by Hallas [39] were used in nine of the 16 studies [24,27,31-35,37,38], and Schumock’s criteria [40] in four [23,29,30,36]. Eight included studies conducted between 1992 and 2009 investigated inpatients’ PADRs that were present during hospital- isation (Table 3) [23,30,41-46]. All studies had a prospective design. Four studies were conducted in Europe [30,43,44,46], one in North America [23] and three in Iran [41,42,45]. The study periods ranged from two weeks [43] to 18 months [44]. Except for one study [46], all used medical records as the source of information, combined to reporting of ADRs or interviewing patients or their family. Five studies were conducted in some wards Table 3. Characteristics of included studies on preventable adverse drug reactions among inpatients. Study (Country) Pearson 1994 [23] (United States){ Gholami 1999 [41] (Iran) Dormann 2004 [30] (Germany){ Baniasadi 2008 [42] (Iran) Davies 2006 [43] (United Kingdom) Davies 2009 [44] (United Kingdom) Pourseyed 2009 [45] (Iran) Farcas 2010 [46] (Romania) Study period 6 months, 1992–1993 4 months, 1996 12 months+6 months for related readmission, no year 12 months, 2006–2007 2 weeks, 2005 6 months, 2005 15 weeks, 2004 12 months, 2009 Study design Prospective, observational Prospective, randomised for inclusion Prospective, observational Prospective, interventional Prospective, observational Prospective, observational Prospective, observational Prospective, observational Population characteristics No age limitation No age limitation, range 10–86 years Mean age 57 years (range 18–97), high proportion of those between 55–70 years No age limitation Median age 61 years (range 45–78), 51% male Median age of people without ADR 61 years Mean age 60 years (range 13–91), 78% between 40–79 years, 51% male Mean age 59 years (range 25–92), 47% male Characteristics of patients with ADRs Mean age unknown, 50% male Unknown Definition for ADR{ Similar to WHO [16] WHO [16] Criteria for preventability Schumock [40] Schumock [40] Unknown Unknown Median age 70 years (range 52–79), 38% male Median age 72 years, 41% male Mean age 54 years, 43% male Mean age 65 years, 31% male WHO [16] Schumock [40] WHO [16] Schumock [40] Edwards and Aronson [17] Edwards and Aronson [17] WHO [16] Hallas [39] Hallas [39] Schumock [40] WHO [16] Imbs [57] ADR = adverse drug reaction; WHO = World Health Organization. {Data from study used for analyses on preventable adverse drug reactions for both outpatients and inpatients. {Studies using WHO’s definition may have referenced another publication for the definition. doi:10.1371/journal.pone.0033236.t003 PLoS ONE | www.plosone.org 5 March 2012 | Volume 7 | Issue 3 | e33236