Controls eliminate alternate explanations of experimental results, especially experimental errors and experimenter bias.

The problem of experimenter bias can be avoided by using blinding:

However, in a 1971 study it was found that there was experimenter bias involved (all of the researchers were male).

The incident is used as a cautionary tale among scientists on the dangers of error introduced by experimenter bias.

It is also in epidemiology that experimenter bias has been better studied than in other sciences.

However the healer involved in the experiment was a personal acquaintance of the study authors raising the distinct possibility of experimenter bias.

Multiple base-line designs are associated with potential confounds introduced by an experimenter bias which must be addressed in order to preserve objectivity.

A priori (beforehand) specification of the hypothesis, time frames, and data limits help control threats due to experimenter bias.

The speech errors were collected by observation which could lead to experimenter bias or human error.

This is done to guarantee that neither mother, nor experimenter bias the infant's response.