Table 4.

Study quality and risk of bias assessment of included studies on local administration of probiotic tablets as lozenges according to the Cochrane Collaboration’s tool.

Study (year)	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective outcome reporting	Other sources of bias	Overall quality*
Keller et al. (2017)	U	U	L	L	L	L	L	Fair
Braathen et al. (2017)	L	L	L	U	L	L	L	Good
Hallstrom et al. (2013)	L	U	L	U	L	L	L	Fair

U; unclear risk of bias, L; low risk of bias, H; high risk of bias.

*Good quality: all criteria met; Fair quality: one criterion not met (i.e. high risk of bias for one domain or two criteria unclear); Poor quality: two or more criteria listed as high or unclear risk of bias.