Most researchers will choose to study individual groups for the convenience of researchers and is trying to prevent the exchange of information between the control group and the experimental group.
Most researchers choose to study one group. For the convenience of the research is to try and prevent the exchange of information between the control group and the experimental group.
Most researchers will choose to study one by one group. For the convenience of the researcher and is trying to prevent the exchange of information between the control group and the experimental group.