Study ID	Domain 1: participant selection	Domain 1 (justification)	Domain 2: subsequent treatment	Domain 2 (justification)	Domain 3: outcome measurement	Domain 3 (justification)	Domain 4: prognostic factor measurement	Domain 4 (justification)	Domain 6: adjustment for other prognostic factors	Domain 6 (justification)
Almuqate 2018	Unclear concerns	Conference abstract: little information	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Bady 2012 (E‐GBM)	Low concerns	No concerns	Low concerns	People received Stupp	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Bady 2012 (M‐GBM)	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Barault 2015	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Barbagallo 2014	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Bell 2017	Low concerns	No concerns	Low concerns	No concerns	Unclear concerns	Note that OS was measured from a later start point than other papers	Low concerns	No concerns	Low concerns	No concerns
Brigliadori 2016	Unclear concerns	People undergoing biopsy were not included in our analysis due to the way data were presented (they are not included in the KM‐curve)	Low concerns	People received Stupp	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Chai 2018 (7‐site cohort)	Low concerns	No concerns	Low concerns	All people received TMZ.	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Chai 2018 (8‐site cohort)	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Dahlrot 2018 (NS cohort)	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Dahlrot 2018 (RSD cohort)	Low concerns	No concerns	Low concerns	Not all people received TMZ but only people that received TMZ are included in the analysis	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Dunn 2009	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Felsberg 2009	High concerns	Study cohort included only people who were treated with open resection and who received ≥ 2 cycles of chemotherapy, thus excluding people with tumour biopsy only or too poor clinical condition for chemotherapy, or both	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Havik 2012	Low concerns	No concerns	Low concerns	Only people treated with radiotherapy + TMZ were included in the analysis	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Hsu 2017 (see Hsu 2015)	Low concerns	No concerns	Low concerns	TMZ with concomitant radiotherapy for all people	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Karayan‐Tapon 2010	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Kim 2016	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Kristensen 2016	Low concerns	All people have glioblastoma	Low concerns	People received Stupp	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Lalezari 2013	Low concerns	1/418 participants did not receive TMZ; 2 died before TMZ	Low concerns	Nearly all people received TMZ, only 1 surviving participant did not	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Lattanzio 2015	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Lechapt‐Zalcman 2012	Low concerns	People had TMZ but additionally got Gliadel	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
McDonald 2013	Low concerns	No concerns	Low concerns	All people received TMZ.	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Melguizo 2012	Unclear concerns	People had to have KPS > 60 to be included	Low concerns	All people received concurrent TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Nguyen 2015	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Park 2011	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Quillien 2014 (test)	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Quillien 2014 (validation)	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Quillien 2016	Low concerns	Frozen samples with a histologically estimated tumour cell content < 40% were excluded from the study	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Thon 2017	Unclear concerns	Special population: unsuitable for GTR	Low concerns	All people were assigned to receive radiotherapy + TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
Yamashita 2018	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Unclear concerns	Unclear whether putting multiple methods of determining MGMT status into the model together would this reflect real practice
Yang 2012	Low concerns	No concerns	Low concerns	All people received TMZ	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	N/A	No concerns
Yoshioka 2018	Low concerns	No concerns	Low concerns	No concerns	Low concerns	Outcome was all‐cause mortality	Low concerns	No concerns	Low concerns	No concerns
GTR: gross total resection; KM: Kaplan‐Meier; KPS: Karnofsky performance status; N/A: not applicable; OS: overall survival; TMZ: temozolomide.