Experimental design

• What are the 3 ways we use participants in an experiment?

  1. Independent measures
  2. Repeated measures
  3. Matched participants
• Independent measures procedures

  1. recruit a group of participants
  2. divide them into 2 groups
  3. the first group will do the experimental task with the IV set for condition 1
  4. The second group will do the experimental task with the IV set for condition 2
  5. measure the DV for each group
  6. Compare the results for the 2 groups
• Matched participants procedures

  1. Recruit a group of participants (A)
  2. Find out what sort of people you have in the group
  3. Recruit another group of participants (B) that matches the participants in A one for one
  4. Treat the experiment as independent measures where one participant from A and one from B have the same characteristics and do the experimental task set for condition 1 (Same for condition 2 with different people, 1 from A and 1 from B)
  5. Compare the results for the matched pairs
• What is the method of allocation to condition for repeated measures?

  The same participants take part in each condition of the experiment
• What is the method of allocation to condition for independent measures?

  Two separate groups of participants, one group in each condition. Participants are allocated to their condition by random allocation
• What is the method of allocation to condition for matched pairs?

  Pairs of participants are matched from sample in terms of key variables such as age and IQ. One member of each pair is then placed in the experimental group and the other member in the control group
• Strengths of repeated measures

  Fewer participants are required, so this is less costly and time consuming

  Reduces participant variables, as the same participants take part in both or all conditions
• Strengths of independent measures

  Avoids order effects and reduces demand characteristics, making the results more vaild
• Strengths of matched pairs

  Avoids order effects and reduces participant variables and demand characteristics, making results more valid
• Weaknesses of repeated measures

  Issues with order effects, such as practice effects or fatigue, as participants take part in both conditions
• Weaknesses of independent measures

  More participants are required and participant variables may affect the results
• Weaknesses of matched pairs

  Impossible to match people exactly unless using identical twins

  More participants are required
• What type of experimental design is the following:

  A study compared the intelligence of a group of children who had been fostered to a group of children who had remained in institutions, paired on age

  Independent measures
• What type of experimental design is the following:

  A study compared the reading ability of children before and after a new intervention program was implemented in a school

  Repeated measures