Final answer:
A placebo is a substance with no therapeutic effect used as a control in studies, and its psychological impact is known as the placebo effect. The main effect is the primary outcome measured in a study. Techniques like random assignment, the double-blind method, and the use of a control group help prevent biases like demand characteristics and practice effects.
Step-by-step explanation:
A placebo is a substance with no therapeutic effect given to a participant in a study as a control to test the efficacy of a treatment. The placebo effect describes a beneficial effect produced by a placebo, which cannot be ascribed to the properties of the placebo itself, and must therefore be due to the patient's belief in the treatment. The main effect refers to the primary response of interest in a study that researchers are trying to measure or observe.
Importance of Specific Experimental Techniques:
Random assignment is a technique used to evenly distribute the characteristics of participants across various groups in an experiment to reduce bias.
The double-blind technique is an experimental procedure where both researchers and participants do not know who has been assigned to which group (e.g., treatment or control), thus minimizing bias due to expectations or behavior.
A control group or condition is used to demonstrate what happens in the absence of the treatment being tested, and often receives a placebo.
Demand characteristics can influence experimental results when participants form an interpretation of the experiment's purpose and subconsciously change their behavior to fit that interpretation. Practice effects occur when participants improve at a task over time simply due to repetition, which can influence results, especially in longitudinal studies.