Table 2 Quality assessment of included studies based on Newcastle–Ottawa Scale
AuthorYearSelectionComparabilityExposure
Hamalainen, 2003 [41]2003312
Tuominen, 2003 [26]2003322
Hung, 2004 [18]2004323
Cabrera, 2005 [12]2005313
Tu, 2007 [25]2007213
Dietrich, 2008 [13]2008323
Padilha, 2008 [22]2008322
Österberg, 2008 [21]2008313
Holmlund, 2011 [16]2011313
Paganini-Hill, 2011 [23]2011323
Hayasaka, 2013 [15]2013312
Schwahn, 2013 [24]2013322
Janket, 2014 [19]2014313
Ando, 2014 [11]2014312
Liljestrand, 2015 [20]2015323
Hu, 2015 [17]2015322
Vedin, 2015 [27]2015322
Joshy, 2016 [6]2016322