Table 3 Assessment of risk of bias of included cohort studies

Criteria

Jethanamest D

Benlyazid A

Owens JM

Krengli M

Meleti M

Temam S

(2011) [6]

(2010) [11]

(2003) [16]

(2006) [14]

(2008) [21]

(2005) [15]

Any criteria descriptions for the patients

yes

yes

yes

yes

yes

yes

The representativeness of the surgery only group

yes

yes

yes

yes

yes

yes

The representativeness of the postoperative radiotherapy group

yes

yes

yes

yes

yes

yes

Group comparable for:

yes

yes

yes

yes

yes

yes

a.average age b.negative margin c patinet status

Group comparable for:

unclear

unclear

unclear

unclear

unclear

unclear

a.tumor site b.radiotherapy plan c.tumor stage

Control for confounding at each outcome(OS)^a

yes

yes

no

unclear

no

unclear

Control for confounding at each outcome(LR)^a

unclear

yes

no

yes

no

unclear

Control for confounding at each outcome(DM)^a

unclear

yes

no

unclear

no

unclear

Blinding of participants at each outcome

yes

yes

yes

yes

yes

yes

Ascertainment of intervention exposure

yes

yes

yes

yes

yes

yes

Blinding of outcome assessment at each outcome

yes

yes

yes

yes

yes

yes

Ascertainment of outcome data

yes

yes

yes

yes

yes

yes

Was follow up long enough for outcomes to occur(OS)

yes

yes

yes

no

yes

yes

Was follow up long enough for outcomes to occur(LR)

no

yes

yes

yes

no

yes

Was follow up long enough for outcomes to occur(DM)

no

yes

yes

no

no

yes

Adequacy of follow up of cohorts

unclear

unclear

unclear

unclear

unclear

unclear

Criteria

Gal TJ

Thariat J

Roth TN

Brandwein MS

Cheng YF

Sun CZ

(2011) [7]

(2011) [10]

(2010) [12]

(1997) [17]

(2007) [13]

(2014) [20]

Any criteria descriptions for the patients

yes

yes

yes

yes

yes

yes

The representativeness of the surgery only group

yes

yes

yes

yes

yes

yes

The representativeness of the postoperative radiotherapy group

yes

yes

yes

yes

yes

yes

Group comparable for:

yes

yes

yes

yes

yes

yes

a.average age b.negative margin c patinet status

Group comparable for:

unclear

unclear

unclear

unclear

unclear

yes

a.tumor site b.radiotherapy plan c.tumor stage

Control for confounding at each outcome(OS)^a

yes

no

no

no

no

yes

Control for confounding at each outcome(LR)^a

unclear

no

no

no

no

unclear

Control for confounding at each outcome(DM)^a

unclear

no

no

no

no

unclear

Blinding of participants at each outcome

yes

yes

yes

yes

yes

yes

Ascertainment of intervention exposure

yes

yes

yes

yes

yes

yes

Blinding of outcome assessment at each outcome

yes

yes

yes

yes

yes

yes

Ascertainment of outcome data

yes

yes

yes

yes

yes

yes

Was follow up long enough for outcomes to occur(OS)

yes

yes

yes

yes

yes

yes

Was follow up long enough for outcomes to occur(LR)

no

yes

yes

yes

yes

no

Was follow up long enough for outcomes to occur(DM)

no

yes

yes

yes

yes

no

Adequacy of follow up of cohorts

unclear

unclear

unclear

unclear

unclear

unclear