Study designs of evaluations included in the review
Only published randomised controlled trials (RCTs) were included in the review.
Specific interventions included in the review
Any kind of spinal manipulation was included in the review. Where described, the types of spinal manipulation included 'manual therapy', chiropractic and osteopathic manipulation.
Participants included in the review
Though not explicitly stated as an inclusion criterion, the included participants appeared to be adults with any type of headache. The studies included participants with migraine, tension-type headaches, 'cervicogenic' headache, 'spondylogenic' headache, and dull, non-throbbing, bilateral headaches.
Outcomes assessed in the review
No inclusion criteria relating to the outcomes were stated. The specific outcomes included in the review were: pain (visual analogue scale), headache pain intensity, headache frequency, OTC use, SF-36, number of headache hours per day, use of analgesics, electromyographic muscle tension levels in frontalis, temperature in dominant hand, daily headache diary, cervical muscle tenderness, and disability.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.