• de Groot FM
• Voogt-Bode A
• Passchier J
• Berger MY
• Koes BW
• Verhagen AP

• Data Interpretation, Statistical
• Headache Disorders / drug therapy
• Headache Disorders / therapy
• Placebo Effect

Method: This is a secondary analysis of randomized controlled trials from 8 systematic reviews and selected trials with a “no treatment” or placebo control group. The different types of “no treatment” and placebo interventions were assessed and classified into 6 subgroups. The analyses were carried out according to type of outcome variable.

Results: In total, 119 studies were included (7119 participants). The mean recovery rate in all control groups was 35.7%. Significantly more participants recovered in control groups of pharmacological studies than in nonpharmacological studies: 38.5% vs 15.0%, respectively. Adults were more likely to recover in nonpharmacological studies and children in pharmacological studies.

Conclusions: The mean recovery rate in the control groups was 36%. The recovery rate varied substantially between type of intervention and patients.

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