A double-blind experiment was conducted to evaluate the effectiveness of the Salk polio vaccine.

The purpose of keeping the diagnosing physicians unaware of the treatment status of the experimental subjects was to

(a) eliminate grounds for malpractice suits.

(b) ensure that subjects were randomly assigned to treatments.

(c) eliminate a possible source of bias.

(d) make sure nobody is harmed.

(e) avoid the placebo effect.

The efficiency of the Salk polio vaccine was tested in a double-blind experiment.

The random assignment method assigns subjects to treatments based on chance. Before the treatments are applied, random assignment establishes treatment groups that are comparable (except for chance variance). In experiments, randomization and comparison combined prevent bias, or systematic favoritism.

A double-blind experiment was done to assess the effectiveness of the Salk polio vaccination in the question. The goal of keeping the diagnosing physicians in the dark about the experimental participants' treatment status was that if they knew what drug was given and how it worked, they could assume it worked better than a placebo, which would show up in their statistics. As a result, option (c) is the correct choice for removing a potential source of bias.