1. Challenges in design and interpretation of chronic pain trials
R.A. Moore, S Derry, P.J. Wiffen 
British Journal of Anaesthesia 
Volume 111, Issue 1, Pages (July 2013)
DOI: /bja/aet126
Copyright © 2013 The Author(s) Terms and Conditions

2. Fig 1
Hypothetical trial in chronic pain with ‘flare’ design. Patients are screened at point S when still taking their usual pain treatment; they then stop that treatment and those with pain increase above 40/100 mm are randomized at point R. Pain levels then fall over about 2–4 weeks on active treatment and will continue at much the same levels over the longer term.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
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3. Fig 2 The design of a classic chronic pain trial.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
Copyright © 2013 The Author(s) Terms and Conditions

4. Fig 3
Response rates (typically at least 50% pain intensity reduction) with active therapy and placebo after 12 weeks of treatment (6 weeks with ankylosing spondylitis) in six chronic pain conditions. *Indicates last observation carried forward imputation method that may overestimate percentage with effective treatment for active compared with placebo.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
Copyright © 2013 The Author(s) Terms and Conditions

5. Fig 4
The design of an EERW chronic pain trial. In order to obtain satisfactory pain relief with tolerable adverse events, an initial dose titration phase gradually increases drug dose to obtain pain relief while minimizing adverse events. Titration can often be over several weeks, mimicking the clinical practice situation.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
Copyright © 2013 The Author(s) Terms and Conditions

6. Fig 5 The design (partial) of an effectiveness trial in chronic pain.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
Copyright © 2013 The Author(s) Terms and Conditions

7. Fig 6 The design of a crossover trial in chronic pain.
British Journal of Anaesthesia  , 38-45DOI: ( /bja/aet126)
Copyright © 2013 The Author(s) Terms and Conditions