Passchier 1990.

Study characteristics
Methods	RCT. 2 arms. Assessed at pretreatment, post‐treatment
Participants	End of treatment: n = 119 Start of treatment: n = 119 Sex: 65 F, 54 M Mean age = 13.7 years (SD 1.4) Source = school Diagnosis = headache (at least weekly) Mean years of pain = none given
Interventions	"Progressive relaxation training" "Placebo physical concentration training"
Outcomes	Primary pain outcome: headache intensity Primary disability outcome: school problems Primary depression outcome: none Primary anxiety outcome: Fear of Failure Headache intensity Headache frequency Headache duration School problems (composite) Fear of failure (from Hermans' Debilitating Anxiety of Achievement Motivation Test)
Notes	COI: not reported Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"The 19 classes of the participating teachers were allocated at random to a Progressive Relaxation Training or a Placebo Training group." Comment: probably done, no method described
Allocation concealment (selection bias)	Unclear risk	No description found in text Comment: probably not done
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No description found in text Comment: probably not done
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts were reported
Selective reporting (reporting bias)	High risk	Data were incompletely reported