Experimental Design

• Independent group design definition:

  • different participants are used in each condition of the independent variable
  • each condition of the experiment includes a different group of participants
  • done by random allocation- equal chance of participants assigned to each group
• Strengths of IGD:

  • avoids order effects as people participate in only one condition, and avoids demand characteristics
  • no boredness or practice effect
• Weaknesses of IGD:

  • time consuming
  • differences between participants may effect results- participant (extraneous) variables
• Repeated measures group design definition: the same participants take part in each condition of the independent variable
• Strengths of RMGD:

  • fewer people needed as they take part in all conditions
  • eliminates participant variables
• Weaknesses of RMGD:

  • there may be order effects- performance in 2nd might be better due to practice effect or worse due to fatigue effect
• Counterbalancing (ABBA) definition:

  • to combat order effects, the research counterbalances the order of the conditions for the participants
  • the order is alternated, which participants perform in different conditions of an experiment
• How to carry out counterbalancing:

  sample split into 2 groups: EXPERIMENTAL GROUP (A), CONTROL GROUP (B)

  • group one does A then B
  • group two does B then A
• Matched pairs design definition:

  • participants are matched according to characteristics such as age, gender and IQ
  • one pair must be randomly assigned to the experimental group and the other to the control group
• Strengths of MPD:

  • reduces participant variables because the researcher has tried to pair up participants so that each condition has people with similar characteristics and abilities
  • avoids order effects
• Weaknesses of MPD:

  • it is impossible to match people exactly, unless identical twins