Psychological Investigations : The experimental method

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  • The experimental method
    • Key features
      • Theory
        • Test
          • Control
            • Replication
              • In order for support for a theory to be retested it is vital that any experiment can be replicated by others
            • Has to be under controlled conditions, to make sure you are finding results due to only an identified variable
          • You have to make sure that the variable you are manipulating has a measurable effect on the  other variable
        • You need a hypothesis to try and prove/disprove
          • Hypothesis
            • Null hypothesis
              • There will be no significant difference  on the performance on a memory test between participants who are tested at 10am and 10pm
            • Alternate hypothesis
              • Two tailed
                • There will be a significant difference in performance between participants tested in the morning and in the evening
              • One tailed
                • Participants will perform better in the morning than in the evening
            • A hypothesis is a testable, predictive statement
    • Designing an experiment
      • Come up with a hypothesis
        • Design an experiment to test the hypothesis
          • Manipulate one factor (IV) that you have identified in the hypothesis to cause a particular effect
            • Measure the effect of this manipulation. The factor that is measured is the DV.
              • Analyse the results from other conditions and compare the mean results. If there is a difference this supports the hypothesis
    • In an experiment there are IVs and DVs
      • In a true experiment the researcher manipulates the IV and in this way creates the different conditions of the experiment
      • The DV is whatever the researcher has chosen to measure as a consequence of the manipulation of the IV.
    • Advantages and disadvantages
      • Experiments are often low in ecological validity as generaly they are controlled situations removed from real life
      • Enables you to test hypotheses.
      • Easily replicated due to standardised procedures
      • Allows researcher to control extraneous variables therefore improving reliability
      • Difficult to orgaise and is not generalisableas sample sizes are usually small
      • Participating in experiments may cause anxiety or stress in participants
    • There are 3 main experimental designs
      • Independent measures
        • Participants are randomly allocated to groups and each group is tested in one condition
          • Group A in condition A. Group B in condition B.
            • E.g. Loftus and Palmer (1974)
        • No order effects
        • Not possible to control participant variables
      • Repeated measures
        • The same participants are tested in two or more conditions. The mean is calculated and if a difference is found, this supports the experimental hypothesis
          • Group A in condition A. Group A in condition B.
        • Potential order effects
      • Matched participants
        • Participants are divided into groups on the basis of matching one or more criteria such as age, gender etc.
          • E.g. Bandura and Ross (1961)
        • Extraneous variables are well controlled
        • Its impossible to control extraneous variables so in practise normally they are only matched on one or two vriables
  • Other variables are controlled
    • Measure the effect of this manipulation. The factor that is measured is the DV.
      • Analyse the results from other conditions and compare the mean results. If there is a difference this supports the hypothesis
  • Removes participant variables
    • Repeated measures
      • The same participants are tested in two or more conditions. The mean is calculated and if a difference is found, this supports the experimental hypothesis
        • Group A in condition A. Group A in condition B.
      • Potential order effects

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