Abdul has volunteered to participate in an experiment evaluating the effectiveness of aspirin. Neither he nor the experimenters know whether the pills he takes during the experiment contain aspirin or are merely placebos. The investigators are apparently making use of:

The double blind procedure

Explanation:

The double blind procedure is an experimental procedure mostly used in fields of research such as medicine, in which half of the participants of an experiment are given a particular medication, while the other half of the participants are given a medication that looks and taste exactly the real medication but it is inert or does not produce any effect as the real medication. The inert medication or treatment is referred to as the placebo. In this type of procedure, neither the participants nor the experimenters have knowledge of who receives the placebo or not. The aim is to prevent placebo effects on the participants and also prevent experimenter biases.

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