Control of Variables

• extraneous variable

  - nuisance variable

  - easily controlled before experiment

  - may compete with the independant variable in explaining the outcome of study

  e.g. age of Ps, time of day
• confounding variable

  - type of extraneous

  - not easily controlled

  - mean you can't be sure what caused the change in DV

  - a problem because it affects both DV & IV

  e.g. personality if Ps, lifestyle
• extraneous and confounding variables can be subdivided into 2 variables


  participant and situational
• demand characteristics


  cues in an experiment that tell the participant what behavior is expected/cause a P to guess the aim of the study
• investigator effects


  Any effect of the investigators behaviour on the research outcome e.g. may smile more at expected responses
• randomisation

  The use of chance wherever possible to reduce the researcher's influence on the design of the investigation.

  e.g. order of words in a list being randomly generated
• standardisation


  making sure all participants are subject to the same environment, information and experience
• participant variables


  Individual differences in the personal characteristics of research participants that may affect the DV
• situational variables

  features of the environment that may affect the DV