Experimental Design and Variables

• Independent Measures Design:

  • A group of participants are recruited and divided into 2.
  • The first group does the experimental task with the IV set for condition 1, and the second group does the experimental task set for condition 2.
  • The DV is measured for each group and the results are compared.
  • Strength:
  • There is no order effects presented.
  • Participants are more likely to guess the aims of the study.
  • Weakness:
  • No control of participant variables.
  • You need more participants.
  • Solution: Random allocation solves the first limitation.
• Repeated Measures Design:

  • A group of participants is recruited and the group does the experimental task with the IV set for condition 1, and then the same for condition 2.
  • The DV is measured for each condition, and the results are compared.
  • Strength:
  • Eliminates participant variables.
  • Not as time consuming as fewer participants needed.
  • Weakness:
  • Order effects presented.
  • Solution: Counterbalancing
• Matched Pairs:

  • A group of participants are recruited.
  • We find out what sort of people we have in a group and recruit another group that matches them one for one.
  • The experiment is then treated like an independent measures design and the results are compared.
  • Strength:
  • No order effects
  • Demand characteristics are less of a problem.
  • Weakness:
  • Time consuming and expensive to match pairs.
  • Difficult to match variables to participants
• Experimental Method:

  • The aim of a study is a statement of what the researcher intends to investigate.
  • The hypothesis of a study is an idea derived from a psychological theory which contains a prediction.
  • Directional Hypothesis: indicated a direction in the prediction (one-tailed)
  • Non-directional Hypothesis: does not indicate a direction in the prediction (two-tailed)
• Variables:

  • Independent variable: The variable that is manipulated.
  • Dependent variable: The variable that is measured.
  • We must use operationalisation to ensure variables are in a form that can be tested.
  • Extraneous Variables:
  • The variables apart from the IV that may influence the DV.
  • Situational Variables are controlled through standardisation.
  • Participant variables are controlled through randomisation.