Table 3.

Rating of the studies with the Downs and Black Scale [10]

Authors	Study types	Score	Quality index
Budgell and Hirano [31]	Rand. cross-over design	16	Moderate
Cardoso-de-Mello-e-Mello-Ribeiro [18]	RCT	18	Moderate
Chiu and Wright [27]	RCT	11	Limited
Curi et al. [8]	RCT	16	Moderate
Fornari [14]	Rand. pilot study	18	Moderate
Fukada et al. [24]	Rand. cross-over design	13	Limited
Gibbons et al. [32]	Rand. pilot study	13	Limited
Giles et al. [29]	Rand. cross-over design	13	Limited
Henderson et al. [7]	Rand. pilot study	17	Moderate
Jowsey and Perry [28]	RCT	18	Moderate
La Touche et al. [19]	RCT	24	Strong
Milnes and Moran [16]	Pilot study	12	Limited
Petersen et al. [26]	RCT	13	Limited
Purdy et al. [30]	Rand. cross-over design	14	Moderate
Roy et al. [20]	RCT	19	Moderate
Ruffini et al. [13]	RCT	23	Strong
Shi et al. [17]	Rand. cross-over design	16	Moderate
Scoppa et al. [15]	Rand. pilot study	10	Limited
Win et al. [21]	RCT	21	Strong
Welch and Boone [6]	CCT	10	Limited
Younes et al. [23]	RCT	20	Moderate
Zhang et al. [27]	Clin. multi-centre study	15	Moderate