The "double-blind" procedure is one of a number of general control procedures that is designed to minimise the EFFECT of two things:

• Experimenter effects, which occur as a result of what the researcher knows about the participant. The researcher may unwittingly treat participants slightly differently based on this knowledge. For example, if a researcher wants to study whether science students differ in numerical SKILLS compared to ART students using a SPECIFIC numerical task, he/she might explain the instructions slightly differently to the different groups based on this knowledge, which may have an impact on how respondents perform on the task. Thus, we cannot know if their performance is based on their numerical skills or whether they were given more/less detailed instruction.
• Demand characteristics, which are details about the study that indicate to the participants how to behave. For example, a researcher wants to establish whether people can detect slight differences in air temperature. If people are TOLD when they will be exposed to cold air and when to warm air, it would be very difficult to discern if their responses are the result of the ability to feel the change in air temperature (which is what the study is about) or whether it is because they were told the air temperature has changed.

The "double-blind" procedure is one of a number of general control procedures that is designed to minimise the effect of two things: