Table 1.

Methodological quality of included studies

Cohort studies
Authors, date	Design	Sampling - Cohort selection		Presence of dysphagia			Confounders		Outcomes	Statistics	Overall quality rating
	Retrospective or Prospective	Recruited from similar population	Cohorts similar at baseline	Measure used valid and reliable	Measured similarly for correct allocation	Groups free of dysphagia at start	Identified	Approp strategies to deal with	Measure used valid and reliable	Approp stats used
Altman et al., 2010 [11]	Retro	+	˜	x	+	˜	+	+	+	+	Moderate
Arnold et al., 2016 [27]	Retro	+	+	+	+	˜	+	+	+	+	Moderate
Bonilha, et al., 2014 [15]	Retro	+	˜	x	+	˜	+	˜	+	+	Moderate
Bradley et al., 2011 [28]	Retro	+	+	+	+	+	+	x	+	+	Low
Chaw et al., 2012 [35]	Pro	+	+	+	+	+	+	˜	+	˜	Low
Chen & Ke, 2016 [36]	Retro	+	˜	+	+	˜	+	+	+	+	Moderate
Falsetti et al., 2009 [37]	Pro	+	˜	+	+	˜	+	x	+	+	Low
Ferraris et al., (2001) [38]	Pro	+	˜	+	+	˜	+	˜	+	+	Low
Genther & Gourin, 2015 [16]	Retro	+	˜	x	+	˜	+	+	+	+	Moderate
Gourin et al., 2015 [17]	Retro	+	˜	x	+	˜	+	+	+	+	Moderate
Guyomard et al., 2009 [39]	Retro	+	˜	+	+	+	+	+	+	+	Moderate
Hogue et al., 1995 [29]	Retro	+	+	+	+	˜	+	+	+	+	Moderate
Holmes et al., 2016 [32]	Retro	+	˜	+	+	+	˜	x	+	+	Low
Macht et al., 2013 [40]	Retro	+	˜	+	+	˜	˜	˜	+	+	Low
Macht et al., 2011 [41]	Retro	+	˜	+	+	˜	+	+	+	+	Moderate
Nilsson et al., 1998 [31]	Pro	+	+	x	+	˜	x	x	+	+	Low
Odderson et al., 1995 [42]	Pro	+	+	x	+	˜	x	x	+	+	Low
Rao et al., 2005 [26]	˜	˜	˜	˜	˜	˜	x	x	+	˜	Very low
Smithard et al., 1996 [12]	Pro	+	+	+	+	˜	+	˜	+	+	Moderate
Teasell et al., 2002 [43]	Retro	+	+	+	+	˜	x	x	+	+	Low
Tian et al., 2013 [44]	Retro	+	+	x	+	˜	+	+	+	+	Moderate
Westergren et al., 1999 [33]	Pro	+	+	+	+	˜	+	x	+	+	Low
Young et al., 1990 [30]	Retro	+	+	x	+	˜	+	x	+	x	Low

Key:

+ completed and reported in study

X not completed in study

˜ unclear whether completed as not reported