experimental design

• there are 3 different types of experimental designs including:

  • repeated measures design
  • independent groups design
  • matched pairs design
• using a repeated measures design means all participants receive all levels of IV (participate in all conditions)
• limitations to repeated measures design

  • order of conditions may affect performance on tasks - use counterbalancing to address
  • participants may have guessed purpose of experiment for second condition which may affect behaviour
• independent groups design is where researcher splits participants into 2 equal sized groups labelled A and B and the results of each group are then compared
• limitations of using independent group design:

  • researchers cannot control effects of participant variables
  • independent groups need greater number of participants
• matched pair design is where researcher matches participants into pairs

  • put one half of paid in group A and other in group B
  • guarantees 2 groups will be similar - differences likely to be down to IV
• matched pair design limitations

  • time consuming and difficult to match participants - need larger group of participants to be able to match everyone
  • still cannot control all participant variables as may not be known to researcher
• there are two ways counterbalancing can take place

  1. AB or BA
  2. ABBA
• AB or BA counterbalancing

  • participants are split into 2 groups
  • group 1: participants complete condition A first then condition B
  • group 2: participants complete condition B first then condition A
• ABBA counterbalancing

  • all participants take part in each condition twice:
  • trail 1: condition A (morning)
  • trail 2: condition B (afternoon)
  • trail 3: condition B (morning)
  • trail 4: condition A (afternoon)

  trails 1 and 4 are compared with trails 2 and 3