Example of Item Analysis

A customer relations manager for a chain of restaurants wants to use a survey to assess customer satisfaction. The restaurant manager tests the survey questions in a pilot study to ensure that the questions consistently measure customer satisfaction. The manager randomly chooses 50 customers, asks them three questions, and records their responses on a 5-point Likert scale, where 1 is Not satisfied/Unlikely and 5 is Very satisfied/Highly likely.

  1. Open the sample data, CustomerSatisfaction.MTW.
  2. Choose Stat > Multivariate > Item Analysis.
  3. In Variables, enter 'Item 1' 'Item 2' 'Item 3'.
  4. Click Graphs and ensure that Matrix plot of data with smoother is selected.
  5. Click OK in each dialog box.

Interpret the results

The high, positive values in the Correlation Matrix table indicate that all the items are highly correlated with each other. The matrix plot also shows that all the items have a linear and positive relationship. The overall Cronbach's alpha is 0.9550, which is greater than the common benchmark of 0.7. Therefore, the manager concludes that all the survey questions are measuring the same characteristic (customer satisfaction).

Item Analysis of Item 1, Item 2, Item 3

Correlation Matrix Item 1 Item 2 Item 2 0.903 Item 3 0.867 0.864 Cell Contents: Pearson correlation
Item and Total Statistics Total Variable Count Mean StDev Item 1 50 3.1600 1.2675 Item 2 50 2.8400 1.3607 Item 3 50 2.9400 1.3463 Total 50 8.9400 3.8087
Cronbach’s Alpha Alpha 0.9550
Omitted Item Statistics Adj. Adj. Squared Omitted Total Total Item-Adj. Multiple Cronbach’s Variable Mean StDev Total Corr Corr Alpha Item 1 5.780 2.613 0.9166 0.8447 0.9268 Item 2 6.100 2.525 0.9134 0.8413 0.9277 Item 3 6.000 2.563 0.8870 0.7869 0.9476

Matrix Plot of Item 1, Item 2, Item 3

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