Example of Item Reliability
In this example, you use an item reliability analysis within the Multivariate platform to evaluate the agreement in the way that three groups of people ranked 30 items according to perceived level of danger. Note that in this type of example, where the values are the same set of ranks for each group, standardizing the data has no effect.
1. Select Help > Sample Data Folder and open Danger.jmp.
2. Select Analyze > Multivariate Methods > Multivariate.
3. Select all the columns except for Activity and click Y, Columns.
4. Click OK.
5. Click the Multivariate red triangle and select Item Reliability > Cronbach’s α.
6. (Optional) Click the Multivariate red triangle and select Scatterplot Matrix to hide that plot.
Figure 3.7 Cronbach’s α Report
The Cronbach’s α results show an overall α of 0.8666, which indicates a high correlation of the ranked values among the three groups. The other table in the Cronbach’s α report gives the value of α when each group is excluded. When the Experts column is excluded Cronbach’s α increases to 0.9021 indicating an even higher correlation of ranked values among only Nonstudents and Students.