Types of Reliability

Reliability of Consistency of What? Observers or raters Tests over time Different versions of the same test A test at one point in time

Inter-Rater or Inter-Observer Reliability Object or phenomenon

Inter-Rater or Inter-Observer Reliability Object or phenomenon Observer 1

Inter-Rater or Inter-Observer Reliability Object or phenomenon Observer 1 Observer 2

Inter-Rater or Inter-Observer Reliability Object or phenomenon ? = Observer 1 Observer 2

Inter-Rater or Inter-Observer Reliability Are different observers consistent? Can establish this outside of your study in a pilot study. Can look at percent of agreement (especially with category ratings). Can use correlation (with continuous ratings).

Test-Retest Reliability Time 1 Time 2

Test-Retest Reliability = Test Time 1 Time 2

Test-Retest Reliability Stability over time Test = Test Time 1 Time 2

Test-Retest Reliability Measure instrument at two times for multiple persons. Compute correlation between the two measures. Assumes there is no change in the underlying trait between time 1 and time 2.

Parallel-Forms Reliability Time 1 Time 2

Parallel-Forms Reliability Form A = Form B Time 1 Time 2

Parallel-Forms Reliability Stability across forms Form A = Form B Time 1 Time 2

Parallel-Forms Reliability Administer both forms to the same people. Get correlation between the two forms. Usually done in educational contexts where you need alternative forms because of the frequency of retesting and where you can sample from lots of equivalent questions.

Internal Consistency Reliability Average inter-item correlation

Internal Consistency Reliability Average Inter-Item Correlation Test

Internal Consistency Reliability Item 1 Average Inter-Item correlation Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Item 1 Average inter-item correlation Item 2 I1 I2 I3 I4 I5 I6 1.00 .89 1.00 .91 .92 1.00 .88 .93 .95 1.00 .84 .86 .92 .85 1.00 .88 .91 .95 .87 .85 1.00 I1 I2 I3 I4 I5 I6 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Item 1 Average inter-item correlation Item 2 I1 I2 I3 I4 I5 I6 1.00 .89 1.00 .91 .92 1.00 .88 .93 .95 1.00 .84 .86 .92 .85 1.00 .88 .91 .95 .87 .85 1.00 I1 I2 I3 I4 I5 I6 Item 3 Test Item 4 Item 5 Item 6 .90

Internal Consistency Reliability Average item-total correlation

Internal Consistency Reliability Average item-total correlation Test

Internal Consistency Reliability Average item-total correlation Item 1 Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Average item-total correlation Item 1 I1 I2 I3 I4 I5 I6 Item 2 I1 I2 I3 I4 I5 I6 Total 1.00 .89 1.00 .91 .92 1.00 .88 .93 .95 1.00 .84 .86 .92 .85 1.00 .88 .91 .95 .87 .85 1.00 .84 .88 .86 .87 .83 .82 1.00 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Average item-total correlation Item 1 I1 I2 I3 I4 I5 I6 Item 2 I1 I2 I3 I4 I5 I6 Total 1.00 .89 1.00 .91 .92 1.00 .88 .93 .95 1.00 .84 .86 .92 .85 1.00 .88 .91 .95 .87 .85 1.00 .84 .88 .86 .87 .83 .82 1.00 Item 3 Test Item 4 Item 5 Item 6 .85

Internal Consistency Reliability Split-half correlations

Internal Consistency Reliability Split-half correlations Test

Internal Consistency Reliability Split-half correlations Item 1 Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Split-half correlations Item 1 Item 1 Item 3 Item 4 Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Split-half correlations Item 1 Item 1 Item 3 Item 4 Item 2 Item 3 Test Item 4 Item 5 Item 2 Item 5 Item 6 Item 6

Internal Consistency Reliability Split-half correlations Item 1 Item 1 Item 3 Item 4 Item 2 Item 3 Test .87 Item 4 Item 5 Item 2 Item 5 Item 6 Item 6

Internal Consistency Reliability Cronbach’s alpha ()

Internal Consistency Reliability Cronbach’s alpha () Test

Internal Consistency Reliability Cronbach’s alpha () Item 1 Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Cronbach’s alpha () Item 1 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 Item 2 Item 3 Test Item 4 Item 5 Item 6

Internal Consistency Reliability Cronbach’s alpha () Item 1 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 Item 2 Item 3 Test SH1 .87 SH2 .85 SH3 .91 SH4 .83 SH5 .86 ... SHn .85 Item 4 Item 5 Item 6

Internal Consistency Reliability Cronbach’s alpha () Item 1 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 Item 2 Item 3 Test SH1 .87 SH2 .85 SH3 .91 SH4 .83 SH5 .86 ... SHn .85 Item 4 Item 5 Item 6  = .85

Like the average of all possible split-half correlations Internal Consistency Reliability Cronbach’s alpha () Item 1 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 .87 item 1 item 3 item 4 item 2 item 5 item 6 Item 2 Item 3 Test SH1 .87 SH2 .85 SH3 .91 SH4 .83 SH5 .86 ... SHn .85 Item 4 Like the average of all possible split-half correlations Item 5 Item 6  = .85

Internal Consistency Reliability - Summary Average inter-item correlation Average item-total correlation Split-half reliability Cronbach’s alpha ()