Reliability

• what is reliability?


  • refers to the consistency of a measure

  • a measure is considered reliable if we get the same result repeatedly

  • a research method is considered reliable if we can repeat it and get the same results
• example of reliability 


  • a ruler would be reliable, as the results could be replicated time after time and the same results would be gained (consistency)

  • some research methods such as laboratory studies have high reliability as they can be replicated and the results checked for consistency
• example of unreliability 


  • an IQ test may be unreliable, if a person sits the test on a Monday and scores 140, and then sits the same test on Friday and scores 90

  • even though it can be replicated, it shows low consistency and therefore is an unreliable test

  • research methods such as case studies and interviews have lower reliability as they are difficult or impossible to replicate, so we cannot check how consistent the results are
• experimental methods


  • lab, field, or natural experiments

  • assess reliability by replicating the experiment

  • reliable study = consistent results each time

  • factors that mean the replication of the study is impossible = low reliability

  • e.g. researcher measures stress levels in residents of a town after an earthquake, it would be difficult to replicate the study as researcher wouldn’t have control over when another earthquake might hit
• non-experimental methods


  • observations, interviews, questionnaires, correlations, content analysis

  • replicated to test for reliability

  • other ways to test their reliability
• test-retest reliability


  • the measure is administered to the same group of people twice

  • if the results on the two tests are similar, the test is said to have external reliability (when a test/study should consistently produce the same results no matter the time given)
• split half reliability 


  • splitting a test into two halves, and comparing the scores in both halves

  • if the results in the two halves are similar, we can assume the test is reliable
• inter-rater reliability


  • if the measure depends interpretation of behaviour, we can compare the results from two or more raters

  • if there is high agreement between the raters, the measure is reliable
• examples of external reliability


  • a simple example would be if a doctor gave two pregnancy tests to a woman and the results came back positive both times - test is reliable

  • another example would be a maths test - if a student took a maths test twice and got similar results, the test is said to have external reliability
• internal reliability 


  • if there is a strong positive correlation between both halves, the test is said to have internal reliability

  • it is looking at the same test - do all parts of the test have consistent results