Studies Study ID Country of participants Sample size Onset age PD Ctr Davila-Ortiz de Montellano et al., 2016 [27 ] Mexico 171 171 — Davis et al., 2016 [28 ] USA 418 150 García et al., 2016 [29 ] Mexico 106 135 Shahmohammadibeni et al., 2016 [30 ] Iran 489 489 — Wang et al., 2016 [31 ] China 296 — — Cheng et al., 2016 [32 ] China 1053 1152 Guella et al., 2016 [33 ] Multicentric 1492 971 Chen et al., 2015 [34 ] China 218 110 Huang et al., 2015 [35 ] China, Australia 402 — — Han et al., 2015 [36 ] China 91 92 — Chen et al., 2015 [37 ] China 1276 846 Gao et al., 2015 [38 ] USA 507 1330 Cardo et al., 2014 [39 ] China 752 489 — Guo et al., 2014 [40 ] China 1011 721 Pan et al., 2013 [41 ] China 515 450 Mata et al., 2014 [42 ] USA 1191 — Markopoulou et al., 2014 [43 ] USA 1098 — 62.2 Emelyanov et al., 2013 [44 ] Russia 244 308 — Wu-Chou et al., 2013 [45 ] Taiwan 626 473 Brockmann et al., 2013 [46 ] Germany 1396 — Chung et al., 2013 [47 ] USA 1098 1098 60.4 Pihlstrøm et al., 2013 [48 ] Norway and Sweden 1380 1295 59.0 Heckman et al., 2012 [49 ] USA 426 769 Ritz et al., 2012 [50 ] USA 232 — — Schmitt et al., 2012 [51 ] Germany 980 1005 Miyake et al., 2012 [52 ] Japan 229 357 Pan et al., 2012 [53 ] China 403 315 Cardo et al., 2012 [54 ] Spain 727 480 — Gao et al., 2012 [55 ] USA 584 1571 Trotta et al., 2012 [56 ] Italy 904 891 Hu et al., 2012 [57 ] China 110 136 Botta-Orfilla et al., 2012 [58 ] Spain 84 — — Mata et al., 2011 [59 ] Spain 1445 1161 Chung et al., 2011 [60 ] USA 1103 1103 62.2 Elbaz et al., 2011 [61 ] Multicentric 5302 4161 — Wider er al., 2011 [62 ] USA, Ireland, Norway 1020 1095 Botta-Orfilla et al., 2011 [63 ] Spain 757 708 — Biernacka et al., 2011 [64 ] USA 1098 1098 62.2 Mata et al., 2010 [65 ] USA 1956 2112 Yu et al., 2010 [66 ] China 332 300 Hu et al., 2010 [67 ] China 330 300 Gatto et al., 2010 [68 ] USA 333 336 — Rajput et al., 2009 [69 ] Canada 452 245 — Sutherland et al., 2009 [70 ] Australia 331 296 Brighina et al., 2009 [71 ] USA 893 893 62.1 Kay et al., 2008 [72 ] USA 1802 2192 — Myhre et al., 2008 [73 ] Netherlands 236 236 — Verbaan et al., 2008 [74 ] Netherlands 295 150 — Brighina et al., 2008 [75 ] USA 833 833 61.9 Ross et al., 2007 [76 ] Ireland 186 186 Winkler et al., 2007 [77 ] Germany, Serbia 397 270 — Goris et al., 2007 [78 ] UK 659 2176 63.0 Hadjigeorgiou et al., 2006 [79 ] Greece 178 186 Mueller et al., 2005 [80 ] Germany 669 1002 Mamah et al., 2005 [81 ] USA 557 557 63.0 Spadafora et al., 2003 [82 ] Italy 186 182 — Izumi et al., 2001 [83 ] Japan 200 250
ID: identification; PD: Parkinson’s disease group; Ctr: control group; SD: standard deviation. 