In an experimental investigation the group that is not manipulated by the researcher and is then compared to the experimental group is called the blank group? fill in the blank.

In an experimental investigation, the group that is not manipulated by the researcher and is then compared to the experimental group is called the control.

There are 2 main type of groups in experimental investigations:

In summary, the group that is not manipulated by researcher during experimental investigations and then compared to the experimental group is known as the control group.

More on research groups can be found here:  

equal distribution i think.