Which of the following experiments would most likely contain experimental bias?

• A. A double-blind study is conducted where neither participants nor experimenters know group assignments.
• B. A researcher randomly assigns participants to control and experimental groups.
• C. A researcher tests a new therapy and only selects participants who are likely to benefit from it.
• D. Participants are selected using a random sampling method from the general population.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand what experimental bias means. Experimental bias occurs when the design, conduct, or analysis of an experiment systematically favors certain outcomes, often due to non-random selection or expectations influencing results.
2. Step 2: Review each option to identify potential sources of bias. For example, a double-blind study minimizes bias by preventing both participants and experimenters from knowing group assignments.
3. Step 3: Recognize that random assignment to control and experimental groups helps reduce bias by ensuring groups are comparable at the start of the experiment.
4. Step 4: Notice that selecting participants who are likely to benefit from the therapy introduces bias because the sample is not representative and may inflate the perceived effectiveness of the therapy.
5. Step 5: Understand that random sampling from the general population helps ensure the sample represents the population, reducing selection bias.