What is the primary purpose of randomization in psychology experiments?

What is the primary purpose of randomization in psychology experiments?

• A. To establish baseline measurements
• B. To control for experimenter bias
• C. To reduce selection bias
• D. To increase sample size

Answer: (C)

Random assignment means every participant has an equal chance of ending up in any experimental condition. This helps ensure the groups are comparable on average, including characteristics you’ve measured and those you haven’t measured. When groups are balanced like this, differences in outcomes are more likely caused by the experimental manipulation itself rather than preexisting differences between participants. That’s why this method specifically targets reducing selection bias and supporting clearer causal conclusions. Baseline measurements come from pretests and aren’t about how participants are assigned. Experimenter bias is best addressed by blinding or other techniques, not by randomization alone. Increasing sample size affects power and precision more than the basic equivalence of groups at assignment.

Random assignment means every participant has an equal chance of ending up in any experimental condition. This helps ensure the groups are comparable on average, including characteristics you’ve measured and those you haven’t measured. When groups are balanced like this, differences in outcomes are more likely caused by the experimental manipulation itself rather than preexisting differences between participants. That’s why this method specifically targets reducing selection bias and supporting clearer causal conclusions.

Baseline measurements come from pretests and aren’t about how participants are assigned. Experimenter bias is best addressed by blinding or other techniques, not by randomization alone. Increasing sample size affects power and precision more than the basic equivalence of groups at assignment.