Final answer:
The best method to avoid subject bias is employing a double-blind design, as it obscures group assignment to both participants and researchers, minimizing both participant expectations and experimenter biases.
Step-by-step explanation:
The best method to avoid subject bias, among the options provided, is D) Employing a double-blind design. In a double-blind study, neither the participants nor the researchers are aware of which group the participants are assigned to (control or experimental), which controls for both participant expectations and experimenter bias. The effectiveness of this method lies in its ability to minimize the placebo effect, where the mere expectation of treatment can lead to perceived or actual changes in the participant. Other methods, such as the use of a control group, random assignment of participants, and counterbalancing, play important roles in experimental design but are specifically targeting issues such as environmental or procedural variability, and not solely subject bias as the double-blind method does.