Table 5. Study validity criteria, study quality scores and levels of evidence for included articles.

Article	Scientific study validity criteria					Training-specific study validity criteria					Study quality score	Level of evidence1
	Randomisation	Control group	Power calculation	Blinding	Outcome measure reporting	Outcome measure selection2	Training feedback	Ecological validity	Reporting of compliance	Follow-up
Fu et al. (2004) [36]	0	0	0	0	1	2	2	2	0	0	7	low
Burk et al. (2006) [37]	0	1	0	0	2	1	2	0	0	2	8	low
Stecker et al. (2006) [38]	1	2	0	0	1	1	2	2	1	2	12	moderate
Sweetow and Sabes, (2006) [39]	1	2	0	0	2	2	2	2	1	1	13	moderate
Burk and Humes (2008) [40]	0	0	0	0	2	2	2	0	0	1	7	low
Miller et al. (2008) [41]	0	2	0	0	2	2	0	0	0	0	6	low
Humes et al. (2009) [42]	0	0	0	0	2	2	2	0	2	0	8	low
Stacey et al. (2010) [43]	0	0	0	0	2	2	2	2	2	0	10	low
Tyler et al. (2010) [44]	0	1	0	0	1	1	2	1	0	1	7	low
Oba, Fu and Galvin, (2011) [45]	0	0	0	0	2	2	2	2	2	2	12	moderate
Barcroft et al. (2011) [46]	1	0	0	0	0	0	0	0	0	0	1	very low
Ingvalson et al. (2012) [47]	0	0	0	0	0	2	0	0	0	1	3	very low
Zhang et al. (2012) [48]	0	0	0	0	2	2	2	2	1	2	11	moderate

Criteria scoring: 0 = flawed or no information from which to make a judgement, 1 = weak information, incorrect use or lack of detail from which to make a judgement, 2 = appropriate use and reporting. Study quality score = sum of scores for scientific and training-specific study validity criteria. 1. Level of evidence: Study quality score of 0–5 = very low, 6–10 = low, 11–15 = moderate, 16–20 = high (adapted from GRADE Working Group, 2004 [35]). 2. Outcome measure selection: to assess generalisation of learning to untrained measure(s) of speech intelligibility, cognition or communication.