In a scientific experiment the group of participants used as a basis of comparison is the

Control group

Explanation:

A control group is a group that is used in a scientific experiment as a basis for comparison. This is in contrast to the experimental group, which is the group that will be given the treatment that we are studying. Having a control group when experimenting allows us to keep track of what "normal" conditions are. This allows us to better understand the consequences of the treatment that we are administering.

Hi there!

Control Group

or

the Placebo group

They are to be compared with the group on which experiment is done

hope it make sense!