Control of Variables

• Extraneous variables


  Variables that interfere with the DV and are unwanted as the only thing that should be affecting DV is IV. Researcher should identify these variables at the start of exp so they can take steps to minimise them.
• Effects of extraneous variables


  These variables somewhat muddy exp but do not confound the findings; can make them harder to detect yet they can be eliminated/manipulated
• Confounding variables


  Change systematically with the IV and can change the DV and results of the experiment if not accounted for. E.g: personality
• Participant's reactivity

  Ppts are not passive and will try to make sense of the new situation they're in and thus, participant reactivity is a high extraneous variable that is quite difficult to control.
• Demand Characteristics


  Certain cues may help ppts interpret what is going on and may lead to ppts second guessing the exp. Could also affect how ppts behave: 'please-U-effect' where ppt performs to please experimenter or 'Screw-U-effect' where ppts sabotages exp
• Investigator effect


  Unwanted influence of the investigator on the research outcome
• Hugh Coolican

  States that these effects include expectancy effects and unconscious cues which may cause there to be a different outcome. Other actions like selection of ppts, materials or instructions are examples of this
• Randomisation

  Helps to minimise the effect of Extraneous or Confounding variables and refers to the use of chance whenever possible to reduce researcher's influence on the design of investigation. When there is a number of different conditions, the order of these conditions should be randomly determines. Alternative is counterbalancing
• Standardisation


  All ppts are subject to same environment, information and experience and standardised instructions which are read out to all ppts.