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Reliability Analysis

Reliability Analysis. Overview of Reliability. What is Reliability? Ways to Measure Reliability Interpreting Test-Retest and Parallel Forms Measuring and Interpreting Internal Consistency. What is Reliability?. Extent to which results are consistent

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Reliability Analysis

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Presentation Transcript

  1. Reliability Analysis

  2. Overview of Reliability • What is Reliability? • Ways to Measure Reliability • Interpreting Test-Retest and Parallel Forms • Measuring and Interpreting Internal Consistency

  3. What is Reliability? • Extent to which results are consistent • Validity is the extent to which the instrument measures what it claims to measure. • A good measurement instrument is both reliable and valid. • Reliability is a prerequisite for validity.

  4. Ways to Measure Reliability • Test-Retest • Parallel (Equivalent) Forms • Internal Consistency

  5. Interpreting Test-Retest and Parallel Forms Reliability • Measured with correlation coefficient (Pearson r) between halves or between tests • Generally an r of .7-.8 is considered good reliability, but it depends on what else is available.

  6. Internal Consistency Reliability • Consistency of items within a measurement instrument • Split-half - divide test items into two groups and obtain a score for each half; correlate the scores • Cronbach’s alpha - average of all possible split-half estimates

  7. Assumptions For Internal Consistency Reliability • Equivalent halves or items • Unrelated measurement errors between halves or items • Items represent the same underlying factor • Items have been transformed if necessary

  8. Interpreting Internal Consistency • Generally an alpha of .70-.80 or higher is considered good reliability. • Look for items which, if removed, would substantially improve the reliability. • It may be necessary to retest and do another reliability analysis to confirm.

  9. Review Question! What is the difference between test-retest and parallel forms reliability?

  10. Choosing Stats Participants are shown photos of individuals who differ in two ways: they either do or not have a noticeable facial scar, and they either do or not have a nose ring. Each participant rates all four types of photos on how likely they would be to offer the person in the photo a job. The researcher wants to know whether the effect of having a facial scar depends on whether or not the person has a nose ring.

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