Reliability & Validity

• Reliability


  The consistency of an experiment
• Internal Reliability


  Refers to the extent the experiment was conducted consistently
• Internal Reliability


  • Did all participants have exactly the same experience?
  • Was there a standardised procedure?
  • Is the study replicable?
• External Reliability


  Refers to the extent to which the study is consistent over time
• Assessing External Reliability


  Test-retest: Participants are tested once, then the same participants are tested again at a later date, and the two sets of scores are correlated
• Validity


  Whether a test measures what it intends to measure
• Internal Validity


  Whether we can say for certain that the independent variable has caused the effect seen in the dependent variable
• External Validity


  The extent to which results can be generalised to other settings, people, and time periods
• External Validity


  • Ecological validity: other settings
  • Population validity: other people within the target population
  • Temporal validity: different time periods
• Maintaining internal validity


  Reduces the realism of the study (external validity)
• Maintaining external validity


  Reduces the internal validity of the study
• The psychologist tries to strike a balance between maintaining the internal validity and the realism (external validity) of the study