Controlling Variables

• Randomisation

  • Randomisation can be used to control extraneous and confounding variables.
  • Refers to the use of chance wherever possible to reduce investigator effects on the result of the study.
  • Example: For a memory test, the words should be randomly generated so the researcher doesn’t influence the order.
• Standardisation:

  • Involves using exactly the same formalised procedures and instructions for all participants in a research study.
  • All participants should be subject to the same environment, information and experience.
  • The procedures should be standardised - there should be a list of exactly what will be done in the study
  • The instructions read to participants should be standardised.
• If you don’t control extraneous variables it will lead to lower internal validity.
• If you don’t control extraneous variables it will lead to lower internal validity.
• Consequence of controlling extraneous variables:

  • The more control a study has the less likely it will reflect the participant‘s true/natural behaviour, lowering external validity.