Experimental Types & Design

• An experiment is when the independent variable is manipulated to test the impact on the dependent variable
• Experimental design is how participants were allocated to one of two conditions
• There are two types of experimental conditions. Experimental conditions is when the experiment takes place, and control conditions is when participants are not exposed to the manipulation and are often used to measure the difference.
• There are three types of experimental design; repeated measures, independent group study and matched pairs.
• Repeated Measures


  Every participant carries out each condition of the experiment. The condition is repeated for each participant.
• Matched Pairs


  When there are different groups and conditions where participants are allocated to each group and condition based on their characteristics which could reduce participant variables.
• Independent Group Design


  Each group of participants does only one condition and the performance of both groups can be measured
• Limitations of Repeated Measures

  There may be things that the participant does, order effects, that will effect recall, such as rehearsal or boredom and they may have demand characteristics. To deal with the order effects, researchers can use 2 different but equivalent tests or counterbalance. To deal with demand characteristics, researchers can create a cover story.
• Limitations of Independent Group Designs

  Individual differences cannot be controlled and become a cofounding variable. More participants are required for an IGD than there would be for repeated measures. To deal with this, researchers can randomly allocate participants to conditions to distribute participant variables.
• Limitations of Matched Pairs

  It is difficult and time consuming to match key variables and it requires participants to be selected from large pools. Only known variables can be matched and there are likely to be other variables that still affect the DV. To deal with the complexity and time constraints, researchers can restrict the number of variables to make it easier. To deal with the matching characteristics, researchers can conduct a pilot study to identify which variables are more important to match.
• There are 4 types of experiment

  • Lab
  • Field
  • Quasi-experiment
  • Natural
• Lab Experiment

  An experiment conducted in a controlled environment and participants are aware that they are taking part.
• Lab Experiment: Strengths and Weaknesses

  Strengths:

  • Control over extraneous variables, high internal validity
  • Ensure that the change in the DV is caused by the IV

  Weaknesses:

  • Demand characteristics
  • Low mundane realism and ecological validity
  • IV and DV may be operationalised in a way they wouldn't in everyday life
• Field Experiment


  An experiment conducted in the natural environment the behaviour would usually take place in but the IV is manipulated by researchers. Participants are unaware they are taking part
• Field Experiment: Strengths and Weaknesses

  Strengths:

  • Participants are less likely to respond to cues in the environment, making the behaviour more natural

  Weaknesses:

  • Less control over extraneous variables unlike a lab experiment
• Natural Experiment


  More of an observation which analyses behaviour without the manipulation of the IV by the researchers.
• Natural Experiment: Strengths and Weaknesses

  Strengths:

  • High external validity
  • Allows research into dangerous situations without creating one (e.g. drug abuse)

  Weaknesses:

  • Can only draw tentative conclusions as it is unclear whether it is the IV directly affecting the DV.
  • May be uncontrolled variables
• Quasi-Experiment


  "Almost" experiment where the independent variable already exists and cannot be manipulated, such as gender and age.
• Quasi-Experiment: Strengths and Weaknesses

  Strengths:

  • Controlled conditions
  • Comparisons between people/groups

  Weaknesses

  • Can't be randomly allocated
  • May be cofounding variables