extraneous variables

• An extraneous variable is any variable other than the IV that may impact the DV if it is not controlled. They are unwanted factors that could negatively affect the data.
• A confounding variable is a type of extraneous variable which changes with the IV. This makes it hard to tell if the DV is changing due to the IV or the confounding variable
• Participant variables

  Variables linked to the people used in the study e.g.

  • Gender
  • Life experiences
  • Age
• Situational variables

  Variables linked to the environment of the study e.g.

  • Noise
  • Time
  • Distractions
• Demand characteristics

  A cue in the experiment which has allowed the pps to guess the aim causing them to change their behaviour
• Investigator effects

  Any effect of the investigators behaviour on the research outcome e.g. interaction with pps, design of study
• Extraneous variables can prevent researchers from finding a direct causal effect between the independent variables (IVs) and measured dependent variables (DVs) set out in an investigation.

  For researchers to be confident that change in the IV will solely affect change in the DV, potential confounds need to be identified and controlled/eliminated; poor control will lead to results with lower reliability.
• Controlling for demand characteristics:

  Deception

  Lying about the aims of the study and/or using distracting questions.

  Single blind procedure:

  The pp is unaware of which condition they are in or the research aims. This prevents the pps from seeking clues about the aims and reacting to them.
• Controlling for investigator effects:

  Inter-rater reliability

  Independent raters rate same behaviour as researcher – check for agreement.

  Double blind procedure:

  Both the pp and the researcher are unaware of the groups and which variable they are under
• Controlling for investigator effects:

  Randomisation

  The use of chance where possible to reduce the investigators influence on the study e.g.

  • Randomise which pps are in which group
  • Randomise the order in which the words are given in a recall task
• Controlling for situational variables:

  Standardisation

  Use the same formalised procedures and standardised instructions for all pps