While many studies report improvements with coloured lenses , the effect size is generally small and /or similar to the improvement found with a placebo condition .
Consistent with previous review s and advice from several professional bodies , we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties can not be endorsed and that any benefits reported by individuals in clinical setting s are likely to be the result of placebo , practice or Hawthorne effects
PURPOSE There are many anecdotal cl aims and research reports that coloured lenses and overlays improve  reading performance .
Here we present the results of a systematic review of this literature and examine the quality of the evidence .
Bias in randomised controlled trials: comparison of crossover group and parallel group designs
The efficacy and side effects of the synthetic cannabinoid nabilone were compared with those of the weak opioid dihydrocodeine in the treatment of chronic neuropathic pain . A r and omised , double blind , crossover trial study design was used . Participants received a maximum daily dose of 2 mg nabilone or 240 mg dihydrocodeine . The trial lasted for 14 weeks and comprised two treatment periods , each of six weeks ’ duration , separated by a two week washout period . Participants were patients with chronic neuropathic pain aged 23 - 84 years , who were recruited using convenience sampling from outpatient units at three hospitals in the United Kingdom . The sample comprised 96 patients , who were r and omised to nabilone ( n=48 ) and dihydrocodeine ( n=48 ) in the first treatment period.1 The main outcome was pain as measured on a visual analogue scale over the final two weeks of each treatment period . Side effects were measured by a question naire . The research ers reported that dihydrocodeine provided better pain relief than nabilone and had slightly fewer side effects , although no major adverse events occurred for either drug . Which of the following statements , if any , are true ? Statements a , b , c , d , and e are all true . The aim of the trial was to compare the efficacy and side effects of nabilone with dihydrocodeine in the treatment of chronic neuropathic pain . A r and omised double blind crossover trial was conducted . Participants received both treatments in succession ,
While many studies report improvements with coloured lenses , the effect size is generally small and /or similar to the improvement found with a placebo condition .
Consistent with previous review s and advice from several professional bodies , we conclude that the use of coloured lenses or overlays to ameliorate reading difficulties can not be endorsed and that any benefits reported by individuals in clinical setting s are likely to be the result of placebo , practice or Hawthorne effects
PURPOSE There are many anecdotal cl aims and research reports that coloured lenses and overlays improve  reading performance .
Here we present the results of a systematic review of this literature and examine the quality of the evidence .