Experimental design

• Repeated measures design:


  All participants receive all levels of IV.
• Independent groups design:


  Participants placed in separate groups. Each group does 1 level of IV.
• Matched pairs design:


  2 groups participants- match them on key characteristics believed to affect performance on DV. 1 member of pair allocated to group A & other to group B. Procedure then same as independent groups.
• Disadvantages of repeated measures design:


  Order effect: order of conditions may affect performance. Also may guess purpose of experiment during 2nd test which may affect behaviour.
• Disadvantages of independent groups design:


  Can't control effects of participant variables ( different abilities or characteristics of each participant). These may act as confounding variables. Also, independent groups need more participants than repeated measures in order to end up with same amount of data.
• Disadvantages of matched pairs design:

  Time consuming & hard to match people on key variables. May have to start with large group of people to ensure they can obtain matched pairs on key variables. Also can't control all participant variables as you can only match on variables known to be relevant- others could actually be important.
• How to deal with disadvantages of matched pairs design?

  Restrict number of variables to match on to make it easier. Conduct pilot study to consider key variables that may be important when matching.
• How to deal with disadvantages of independent groups:

  Randomly allocate participants to conditions which (theoretically) distribute participant variables evenly.
• How to deal with disadvantages of repeated measures?


  Counterbalancing deals with order effects. Cover story about study purpose can be used to avoid participants guessing aims of study.
• What is counterbalancing?


  Ensures each condition in repeated measures design is tested first or second in equal amounts. Deals with order effects.