1. Combination Analgesic Efficacy
Jayne E Edwards, DPhil, Henry J McQuay, DM, R.Andrew Moore, DSc 
Journal of Pain and Symptom Management 
Volume 23, Issue 2, Pages (February 2002)
DOI: /S (01)

2. Fig. 1 Mean pain relief score over time in dental pain.
Journal of Pain and Symptom Management  , DOI: ( /S (01) )

3. Fig. 2
Number-needed-to-treat to obtain at least 50% pain relief with single-dose oral analgesics compared with placebo in moderate to severe postoperative pain over 6 hours. Information was from trials of tramadol plus acetaminophen.
Journal of Pain and Symptom Management  , DOI: ( /S (01) )

4. Fig. 3
Number-needed-to-treat to obtain at least 50% pain relief over 4–6 hours. Comparison of single-dose oral tramadol and tramadol plus acetaminophen with other combination drugs and their components. Additional information was from published systematic reviews.
Journal of Pain and Symptom Management  , DOI: ( /S (01) )