control of variables

• what are extraneous variables 


  unwanted extra variables that may affect relationship between the iv and the dv
• what are confounding variables 


  variables other than the iv that may have affected the dv so we cannot be sure of the true nature of change to the dv they vary systematically
• what are demand characteristics 


  any cue from the researcher that may be interpreted by participants as revealing the purpose of the investigation
• two effects of demand characteristics 


  • please U effect: you want to support the researcher and act how you think they want you to
  • screw U effect: you under perform to sabotage the results of the experiment
• what are investigators effects 


  any effects of the investigators behaviour on the research outcome
• how do we control for extraneous and confounding variables 


  • randomisation: using chance during an investigations design and they are decided randomly
  • standardisation: using exactly the same formalised procedures and instructions for all participants
• how do we deal with participant variables 


  systematic method: first come first serve

  random method: flipping coins, this may lead to more in one group
• how do we deal with order effects: counterbalancing 


  tries to control order effects, instead of participanrs all doing same condition at same time, complete them at different times