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Single-Blind Study
A single-blind study occurs when the participants are deliberately kept ignorant of either the group to which they have been assigned or key information about the materials they are assessing, but the experimenter is in possession of this knowledge. Single-blind studies are typically conducted when the participants’ knowledge of their group membership or the identity of the materials they are assessing might bias the results. However, there are situations where creating such ignorance might be impossible or unethical, and in others, it might be advisable for more than the participants to be kept unaware of the test conditions. This entry discusses the single-blind study in relation to the unblinded (neither experimenter nor participants are kept ignorant) and double-blind study (both experimenter and participants are kept ignorant). It also presents some illustrative examples and examines the advantages and disadvantages of the single-blind study.
The Unblinded Study
To understand the blind study, it is advisable first to consider the unblinded study. In this, both participant and observer are fully aware of the groupings and/or materials. For example, a group of patients might be fully aware of which of two types of treatment they are receiving, such as in judging a group of singers in a competition, the participants are fully aware of the identity of each singer. Sometimes, an unblinded study is unavoidable. For example, many routine clinical treatments are done in an unblinded manner, with the patient and therapist actively discussing all the methods available before choosing one. Accordingly, any naturalistic, purely observational study of such a situation will of necessity have to accept that the participant is aware of what is taking place. Likewise, in some circumstances, asking participants to make judgments will also require them to know the identity of what is being judged (e.g., judging the relative merits of famous singers). The unblinded study is, thus, in some instances unavoidable. In practical terms, it is also generally far easier to run than a blind study, which requires greater organization.
However, the unblinded study also carries disadvantages that sometimes outweigh its merits, and experimenters will usually avoid it when a blind study is a viable alternative. At its most basic, the unblinded study provides the participant with information about how they are grouped or what they are assessing, and this knowledge might lead to self-expectations of how they should respond. This can potentially distort results, as is discussed next.
Illustrative Examples
In contrast to unblinded studies, single-blind studies deliberately withhold key information from the participants (though not the experimenters). A commonplace example of withholding key information about test materials is a measure of consumer preference where the participant is asked to judge which of two or more brands of the same basic product is preferred, but the brand identities of the products are hidden from the participant. For example, in comparing the quality of different hi-fi components, products could be hidden behind visually opaque but acoustically transparent material, and the participants could be asked to listen to music played over these systems without being aware of the brands of product. All the participant can do is judge the quality of what they hear. However, the experimenters are aware of the true identity of each piece of equipment being assessed. An example of participants lacking knowledge of which group they belong to is the common clinical procedure where patients are given one of two or more drug treatments, but they do not know which one. However, the experimenters providing the treatments and assessing the treatment are aware of this information.
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