Counterbalancing, in the simplest case of two conditions, is used to remove bias caused by what?

• A. Practice effects
• B. Placebo effects
• C. Demand characteristics
• D. Measurement error

Answer: (A)

Counterbalancing in a two-condition design targets order effects—the bias introduced by the sequence in which conditions are presented. The simplest form is to have half the participants experience condition A first, then condition B, and the other half experience B first, then A. This spreads any learning or fatigue that comes from doing one task before the other across both conditions. As a result, improvements (practice effects) or declines due to fatigue balance out, so the comparison between the two conditions reflects the actual manipulation rather than the order in which they were encountered. Other biases like placebo effects, demand characteristics, or measurement error aren’t what counterbalancing primarily fixes, so the most appropriate choice is practice effects.