Control of variables

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  • Control of Variables
    • Extraneous variables
      • Key to the experiment is that the IV is changed to see how this affects the DV
      • Other unwanted variables are called extraneous variables and should be minimized
      • Some are easy to control such as the age of participants, lighting in the lab - 'nuisance variables
    • Randomisation
      • Minimise the effects of of extraneous/confounding variables
      • Reducing the investigators influence - trying to control investigator effects
      • Conditions should be randomly determined
      • If all participants took part in all conditions the other of these conditions need to be randomized for each participant
    • Confounding variables
      • Do change with the IV
      • Such as personality
    • Investigator effects
      • Participant reactivity leads to investigator effects
      • Unwanted influence of the investigator on the research outcome
      • Can include expectancy effects and unconscious cues
      • May refer to any actions of the researcher that are related to the studies design
    • Demand characteristics
      • Participant reactivity is a significant extraneous variable
        • Difficult to control
      • Participants are trying to work out what is going on in a new situation
        • They may 'second guess' experimenter's intentions as well as the aims of the study
      • May look for cues to tell them how to behave in the experimental situation
        • May perform to please the experimenter or under-perform to sabotage the results of the experiment
    • Standardisation
      • All participants should be subject to the same environment, information and experience
      • Standardised instructions are read to each participants so that non-standardised changes do not act as extraneous variables


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