In a double-blind study, neither the subject nor the researcher will know which treatment the subject is receiving. In many cases, a double-blind study is preferable to a single-blind study, since the researcher cannot
inadvertently affect the results or their interpretation by treating a control subject differently… Learn about this topic in these articles:
control group studies
therapeutic regimens
Such a study is “double-blind”: it controls for both possible tendencies by comparing an active drug with an inactive placebo [an inert drug]. Neither the patient nor the physician knows which drug the patient is taking, so that neither one’s bias can influence the result. Although this is the…
Read Morework of Beecher
- In Henry Knowles Beecher
…to recognize the importance of double-blind placebo-controlled clinical trials [in which neither subject nor doctor know whether the subject will receive a drug or a placebo]..
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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 ...
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Blinding techniques are also used to avoid bias. In a single-blind study the participants do not know what treatment groups they are in, but the researchers interacting with them do know. In a double-blind study, the participants do not know what treatment groups they are in and neither do the researchers who are interacting with them directly. Double-blind studies are used to prevent researcher bias.
Blinding Procedure employed in research to prevent bias in which the participants and/or the researchers interacting with the participations do not know which treatment each case is receiving
Single-Blind Study Research study in which the participants do not know the treatment group that they have been assigned to
Double-Blind Study Research study in which neither the participants nor the researchers interacting with them know which cases have been assigned to which treatment groups
Example: Yogurt Tasting Section
Researchers are comparing a low-fat blueberry yogurt to a high-fat blueberry yogurt. Participants are randomly assigned to receive one type of yogurt. After tasting it, they complete an online survey. The researchers know which yogurt containers are low-fat and which are high-fat, but participants are not told. This is an example of a single-blind study because the researchers know which participants are in the low- and high-fat groups but the participants do not know. A double-blind study may not be necessary in this case since the researchers have only minimal contact with the participants.
Example: Caffeine Energy Study Section
Researchers want to know if adult males who consume high amounts of caffeine interact more energetically. They obtain a representative sample and randomly assign half of the participants to take a caffeine pill and half to take a placebo pill. The pills are randomly numbered and coded so at the time the researchers do not know which participants have been given caffeine and which have been given the placebo. All participants are told that they may have been given a caffeine pill. After taking the pill, researchers observe the participants interacting with one another and rate the interactions in terms of level of energy.
This is a double-blind study because neither the researchers nor the participants know who is in which group at the time the data are collected. After the data are collected, researchers can look at the pill codes to determine which groups the participants were in to conduct their analyses. A double-blind study is necessary here because the researchers are observing and rating the participants. If the researchers know who is in the caffeine group they may be more likely to rate their levels of energy as very high because that is consistent with their hypothesis.