For example, lesions can be photographed before and after treatment and assessed by someone not involved in running the trial. Such blind assessment of outcome can often also be achieved in trials which are open (non-blinded). In a double blind trial it is implicit that the assessment of patient outcome is done in ignorance of the treatment received. In trials of different styles of patient management, surgical procedures, or alternative therapies, full blinding is often impossible. Single blind trials (where either only the investigator or only the patient is blind to the allocation) are sometimes unavoidable, as are open (non-blind) trials. For example, if we want to compare two medicines, one presented as green tablets and one as pink capsules, we could also supply green placebo tablets and pink placebo capsules so that both groups of patients would take one green tablet and one pink capsule.īlinding is certainly not always easy or possible. In studies comparing two active compounds, blinding is possible using the “double dummy” method. Even colour of medication has been shown to influence efficacy. Differences in taste, smell, or mode of delivery may also influence efficacy, so these aspects should be identical for each treatment group. Patients may well see the treatment being given to patients in the other treatment group(s), and the appearance of the drug used in the study could give a clue to its identity. Blinding means more than just keeping the name of the treatment hidden. In a double blind trial neither the patient nor the caregivers are aware of the treatment assignment. For example, the decision to withdraw a patient from a study or to adjust the dose of medication could easily be influenced by knowledge of which treatment group the patient has been assigned to. Similarly, medical staff caring for patients in a randomised trial should be blinded to treatment allocation to minimise possible bias in patient management and in assessing disease status. Blinding patients to the treatment they have received in a controlled trial is particularly important when the response criteria are subjective, such as alleviation of pain, but less important for objective criteria, such as death. The relevance of blinding will vary according to circumstances. In controlled trials the term blinding, and in particular “double blind,” usually refers to keeping study participants, those involved with their management, and those collecting and analysing clinical data unaware of the assigned treatment, so that they should not be influenced by that knowledge. This sort of blinding, better referred to as allocation concealment, will be discussed in a future statistics note. It is a tenet of randomised controlled trials that the treatment allocation for each patient is not revealed until the patient has irrevocably been entered into the trial, to avoid selection bias. Blinding (sometimes called masking) is used to try to eliminate such bias. In research there is a particular risk of expectation influencing findings, most obviously when there is some subjectivity in assessment, leading to biased results. Human behaviour is influenced by what we know or believe. b ICRF Medical Statistics Group, Institute of Health Sciences, Oxford OX3 7LF.a Leo Pharmaceuticals, Princes Risborough, Buckinghamshire HP27 9RR.Douglas G Altman b, professor of statistics in medicine.Simon J Day a, manager, clinical biometrics,.However, higher income countries contributed most often to the journals studied even among journals based outside the US. There was no significant difference in country-of-origin representation between single-blind journals and double-blind journals. This held true even for journals established outside the United States (US=11/12, England = 11/12). The US (n = 16, 100%) and England (n = 16, 100%) most commonly made the top 10 lists for article contribution. 21) when assessing the top eight double-blind journals matched with single-blind journals of a similar impact factor. However, there was no difference for both country of origin (SB = 38.0%, DB = 26.6%, p =. 49), but there was a significant difference between the percentage of articles from the US (SB = 48.0%, DB = 22.8%, p =. There was no difference in the percentage of articles published from the journal's country of origin between the top single-blind journals and double-blind journals (SB = 42.0%, DB = 26.6%, p =. To assess whether the type of peer-review (single-blinded vs double-blinded) has an impact on nationality representation in journals.Ī cross-sectional study analyzing the top 10 nationalities contributing to the number of articles across 16 ophthalmology journals.
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