Controls for Experimental Designs

• One problem with independent groups design is individual differences:

  • There are different participants in each condition, so in one condition the participants may have a particular trait that makes them perform better at the DV (AO2)
• To control for individual differences, random allocation should be used:

  • WHY: This ensures that each participant has the same chance of being in one condition as any other conditions, therefore it is unlikely that all participants in one condition will share characteristics to perform better at the DV
  • HOW: Write down the names of the participants on equal sized pieces of paper, put the paper in a hat, randomly pick out names and place half in condition 1 and the other half in condition 2 (AO2)
• One problem with repeated measures design is order effects:

  • Participants take part in all conditions so may perform better at the second condition (due to practice) or worse in the second condition (due to fatigue) or the first condition may have lasting effects on the second condition (AO2)
• To control for order effects, counterbalancing (ABBA) should be used:

  • WHY: To control and reduce order effects
  • HOW: Half the participants complete condition A then condition B (AO2), the other half complete condition B then condition A (AO2), order effects are balanced/distributed across both conditions