If the experimenter knows who is in the experimental and control groups and treats them accordingly, she runs the risk of .

Experimenter bias

Explanation:

If the experimenter knows who is in the experimental and control groups and treats them accordingly, she runs the risk of Experimenter bias.

Definitions of Experimenter bias

1) Research bias, also called experimenter bias, is a process where the scientists performing the research influence the results, in order to portray a certain outcome.

2) Observer bias (also called experimenter bias or research bias) is the tendency to see what we expect to see, or what we want to see. When a researcher studies a certain group, they usually come to an experiment with prior knowledge and subjective feelings about the group being studied.

this would be about 43%