The subjects in a blind study have no idea whether they are in the control or experimental group. Pharmaceutical research is a good example of this, where companies testing new compounds give some patients the medication at various dosages while giving others placebos with no medical effect. The goal of concealing study information from participants is to avoid bias, in which participants’ behaviors or reactions are influenced by what they know about the study conditions. This may raise some ethical concerns, which should be addressed through careful study design.
The experiment’s researchers are aware of how the participants were grouped and which group each subject belongs to. In some cases, this can lead to experimenter bias, as researchers may have expectations that they project onto participants. For example, a nurse who knows a patient is receiving a placebo may act differently than if the patient is receiving the medication. In some studies, both the experimenters and the subjects must be kept in the dark, which is referred to as a double blind study.
Participants are not given any information about their role in the study and are sorted at random. Experimenters use a variety of sampling techniques to get a good mix of subjects that will accurately reflect the population under study. Random number generators or similar systems can be used to assign people to groups once a blind study participant group has been finalized. This can also help with bias issues; for example, if the assignments are random, an experimenter who likes a participant can’t assign that participant to the group receiving an active medical compound.
The designers of a blind study with human subjects may need to meet with an ethics committee or board before proceeding. They talk about what they’re going to study and the advantages it will provide, as well as the study’s design. This could include a discussion of specific ethical issues. Giving patients a placebo instead of an active drug, for example, may put them at risk, and this must be taken into account when designing studies and obtaining informed consent from participants.
Because of the reduced bias, double blind studies are preferred for many scientific tests when possible. In some cases, concealing the specifics of a study can be difficult, as the nature of the study can be difficult to conceal. For example, scientists studying the benefits of massage don’t have a readily available placebo for study participants, who will be able to tell whether they are getting massages or not.