Control of Variables

• what are extraneous variables?

  • Any variable in a study which could potentially influence the DV other than the IV.
  • do not systematically vary with the IV, they may make identifying a trend more difficult.
  • Participant Variables – Age, Intelligence, Gender.
  • Situational Variables – Time of Day, Temperature of the lab, Noise.
• what are confounding variables?

  • Any variable, other than the IV which may affect the DV but varies systematically with the IV.
  • For example, in the caffeine-stress study, it could have happened that the first 10 participants who arrive at the study are allocated the caffeinated drink. These 10 participants are more anxious personality types. We therefore do not know if increased stress levels in this group are as a result of the caffeine consumption or their personality type.
• what are demand characteristics?

  • Demand characteristics result from cues which arise from the researcher or the research situation which may lead a participant to respond in a certain way during the experiment.
  • Participant reactivity is a difficult variable to control – participants often try to work out the aim of the investigation.
  • The ‘please you effect’ or the ‘screw you’ effect may also occur.
• what is investigator/observer bias?

  • The investigator may be affected by his or her expectations for the study and their hypothesis. This could affect their interaction with participants.
  • For instance, in the stress-caffeine study, the investigator may be more hostile with the caffeine group which could make them more uneasy, or may just be likeable or not according to different people!
  • The experimenter may give away too much information leading to demand characteristics (so must be careful about instructions and standardisation!)
• what is standardisation?

  • All participants should be subject to the same environment, information and experience.
  • This can be aided with standardised instructions which should be read out to participants in a set way.
• what is randomisation?

  • This is the use of chance wherever possible in order to reduce the researcher’s influence on the design of an investigation.
  • Random allocation of participants to conditions.
  • Random generation of stimuli