Extraneous Variables

• Extraneous Variables = Factors which can influence the DV other than the IV
• Psychologists do not want these variables to effect the DV as they are interested in the effect the IV has on the DV.
• Researchers try to control extraneous variables as much as they can.
• Investigator Effects:

  • Involves anything the investigator does that has an effect on a participant’s performance in a study other than what was intended.
  • Referred to as investigator or experimenter bias.
  • Includes direct effects (e.g. smiling or spending more time with one group) and indirect effects (e.g. the design of the study).
  • Can also include the way questions are asked (leading questions).
• Demand Characteristics:

  • Involves participants acting on cues or looking for clues that influence how they behave.
  • They may act in a way that they think is expected and over-perform to please the experimenter (Please-U effect).
  • They may deliberately under-perform to sabotage the results of the study (Screw-U effect).
  • Either way, participant behaviour is no longer natural.
  • Participants may also behave in a way they see as socially desirable.
• Participant Variables:

  • Certain characteristics associated with participants (not the way they behave due to demand characteristics).
  • This can include age, gender, intelligence, motivation, personality, experience.
  • It is important to overcome any participant variables that may act as an extraneous variable so that it doesn’t affect the experiment/study.
• Situational Variables:

  • Factors associated with the environment that could have an effect on the study.
  • Examples: noise, lighting, time of day, heat.
• Confounding Variables:

  • Type of extraneous variable.
  • They vary systematically with the IV and often occur as a result of an extraneous variable not being controlled.
  • Extraneous variables DO NOT systematically vary with the IV.