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Effective Participant Assignment Strategies in Experimental Designs

Understanding the methods to assign participants to different conditions is crucial in experimental research. Between-Subject designs involve assigning different individuals to each level of the independent variable, providing advantages like non-contamination of results but facing challenges of group inequivalence. Within-Subject designs use the same individuals for each level, offering efficiency and reduced subject variance. Counterbalancing techniques like Blocked and Latin Square Designs help control for order effects and sequence, improving research validity. Counterbalancing strategies like Repeated Block Designs and ABBA designs further enhance experimental design precision.

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Effective Participant Assignment Strategies in Experimental Designs

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  1. ASSIGNING PARTICIPANTSTO CONDITIONS • Between-Subject designs • Different people at each level of the IVXA: P1, P2, P3XB: P4, P5, P6 • Advantage • Exposure to one level can’t contaminate performance on the other(s) • Disadvantage • Groups may not be equivalent, even with “random” assignment

  2. Within-Subject designs • Same people receive each level of the IVXA: P1, P2, P3XB: P1, P2, P3 • Advantages • More efficient • Each S serves as their “own control” • Eliminates subject variance from stats • Disadvantages • Exposure to one condition may influence performance in others • Order and carryover effects

  3. Counterbalancing • Blocked designs • Order of conditions is varied over participants • Complete counterbalancing: Subgroup 2 IV levels 3 IV levels etc. 1 AB ABC2 BA ACB 3 BAC 4 BCA 5 CAB5 CBA

  4. Complete counterbalancing (contd) • Advantages • Controls for order effects; each level appears at each order same amount • Allows for order effects to be assessed • Disadvantages • Back to multiple “groups” and inefficiency • Doesn’t control for “asymmetric transfer”

  5. Latin Square Designs • Put each level in each position, counterbalancing order and sequenceSubgroup 1st 2nd 3rd 4th 1 A B C D 2 B D A C 3 D C B A 4 C A D B • Advantage • Much more efficient than complete counterbalancing • Disadvantages: • May miss complex order effects • Still doesn’t control for asymmetric transfer

  6. Counterbalancing • Repeated Block Designs • Each participant gets two (or more) blocks of each condition, intermixed • ABBA designs • ABBA / BAAB designs • Completely randomized block designs • AABABCCBABAAB….. • May be effects of random vs. blocked

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