control of variables

• What is an extraneous variable?


  Variable which might affect DV and happens during the investigation. Can be referred to as uncontrollable variables.
• A confounding variable is a variable that has definitely affected the DV and has already happened before the investigation.
• Situational variable stems from environment e.g noise, temperature, time of day.
• Participant variable stems from ways in which the participants differ from each other e.g IQ, age, gender.
• Demand characteristics is when the participant will try to figure out what is going on in the experiment
• Investigators effect is the investigators behaviour which can be done through non verbal communication.
• 'Please you effect': when the participant acts in a way they think is expected from them
• 'Screw you' effect: the participant may try and sabotage the experiment.
• How can we control extraneous and confounding variables?


  By randomisation or standardisation.
• Randomisation:

  • use of the chance to reduce the investigator's influence on the design of investigation.
  • e.g. memory study: placing names in hat or computer based generator.
• Standardisation:

  • using same procedures and instructions for all participants.
  • to be able to replicate- scientific and objective.
  • PPs given same info, environment