In many experiments the researcher can specify the nature of the participants,the independent variable,the dependent variable,and many situational stimuli that may influence the results.
Before considering some specific issues raised by this article,note that among positive attributes of field techniques is the fact that they can be conducted in the participant's natural setting,
with little disturbance of his or her normal behavior. This tends to enhance the credibility(and external validity)
In some forms of field research,the person is unaware that he or she is a participant.