Simpson 1966.

Methods	Design: Cross‐over study Number of centres: 1 Treatment duration: each treatment period was 4 weeks Flare design: No Wash‐out period: No Time pointof assessments: BL, 4, 8 weeks
Participants	Inclusion criteria: 1. X‐ray evidence of involvement of sacroiliac joints, small joints of the hand were not involved; 2. Chest expansion had to be limited and morning stiffness present; 3. Latex test had to be negative; 4. Serum uric acid level not be in excess of 6.5 mg/100 mL; 5. Raised ESR. Exclusion criteria: None reported. Classification: NA Phenylbutazone (300 mg): Number of participants: 7 Number of completers: 6 Flufenamic acid (600 mg): Number of participants: 7 Number of completers: 7 All participants: Age (mean): males 35, females 51 Male (%): 79 Symptom duration: NA Disease duration: NA HLA‐B27 positive (%): NA
Interventions	Phenylbutazone (300 mg) vs Flufenamic acid (600 mg) Co‐medication: Not reported
Outcomes	Extracted outcomes: Pain on Likert scale Withdrawals due to adverse events
Notes	For the outcome pain on Likert scale individual patient data that were presented in the paper were combined for the meta‐analysis to a mean and SD.Funding source: Not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"… and the order of administration was randomized." No information on sequence generation was provided.
Allocation concealment (selection bias)	Unclear risk	No information was provided on allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"Matched capsules containing flufenamic acid 100 mg and phenylbutazone 50 mg were administered at the rate of six capsules per day."
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No information was provided on blinding of outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	The number of missing observations were low (extracted from table 1).
Selective reporting (reporting bias)	Low risk	All outcomes stated in the methods were reported in the results.
Other bias	High risk	No information provided how statistical analyses were performed. Unable to determine BL characteristics imbalance.