How do experimental and control groups differ? Explain with the help of an example.
Experiments generally involve one or more experimental groups and one or more control groups. An experimental group is a group in which members are exposed to independent variable manipulation. A control group is a comparison group that is treated in every way like the experimental group except that the manipulated variable is absent in it.
The key difference between the two groups lies in the presence or absence of the independent variable. While the experimental group receives the experimental manipulation, the control group does not. This allows the researcher to compare results and establish cause-effect relationships between variables.
For example, in the study by Latane and Darley, participants were sent to three types of rooms. In one room, no one was present — this was the control group. In the other two rooms, two persons were already seated — these were the experimental groups. One experimental group was instructed not to do anything when smoke filled the room, while the other was not given any instructions.
Except for the experimental manipulation, other conditions are kept constant for both groups. The speed with which smoke entered the rooms, the total amount of smoke, and physical conditions were similar for all three groups. The distribution of participants is done randomly, ensuring each person has an equal chance of being included in any group.
Explanation
This answer draws directly from the textbook context which clearly defines experimental and control groups. The Latane and Darley study is the primary example given in the NCERT textbook to illustrate this concept. The answer also incorporates the important point about keeping conditions constant except for the manipulated variable, and the use of random distribution of participants — both crucial aspects of experimental design mentioned in the context.