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 .
The Hawthorne Effect: a randomised, controlled trial
Background The ' Hawthorne Effect ' may be an important factor affecting the generalisability of clinical research to routine practice , but has been little studied . Hawthorne Effects have been reported in previous clinical trials in dementia but to our knowledge , no attempt has been made to quantify them . Our aim was to compare minimal follow-up to intensive follow-up in participants in a placebo controlled trial of Ginkgo biloba for treating mild-moderate dementia . Methods Participants in a dementia trial were r and omised to intensive follow-up ( with comprehensive assessment visits at baseline and two , four and six months post r and omisation ) or minimal follow-up ( with an abbreviated assessment at baseline and a full assessment at six months ) . Our primary outcomes were cognitive functioning ( ADAS-Cog ) and participant and carer-rated quality of life ( QOL-AD ) . Results We recruited 176 participants , mainly through general practice s. The main analysis was based on Intention to treat ( ITT ) , with available data . In the ANCOVA model with baseline score as a co-variate , follow-up group had a significant effect on outcome at six months on the ADAS-Cog score ( n = 140 ; mean difference = -2.018 ; 95%CI -3.914 , -0.121 ; p = 0.037 favouring the intensive follow-up group ) , and on participant-rated quality of life score ( n = 142 ; mean difference = -1.382 ; 95%CI -2.642 , -0.122 ; p = 0.032 favouring minimal follow-up group ) . There was no significant difference on carer quality of life . Conclusion We found that more intensive follow-up of individuals in a placebo-controlled clinical trial of Ginkgo biloba for treating mild-moderate dementia result ed in a better outcome than minimal follow-up , as measured by their cognitive functioning . Trial registration Current controlled trials : IS RCT
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 .