How to know whether a set of Likert items form two scales using SPSS? How to assess the relationship between these two scales? I have designed a questionnaire which has 16 Likert item questions; from 1 (strongly disagree) to 5 (strongly agree). The 16 Likert item  questions are divided into 2 groups: 10 questions for customer loyalty, and 6 for customer satisfaction. 


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*How do I know whether the Likert items should be grouped into the two scales?

*How can I calculate the relationship between the two scales?
 A: You probably want to do exploratory (or possibly confirmatory) factor analysis to check that all items can be scored in terms of your two theorised scales. This could be combined with reliability analysis. You would then score your two scales and then obtain the correlation between the two scales.
I have a tutorial which describes this process using SPSS including scoring the scales.
If you wanted to study latent variables and the measurement model of the test you could use structural equation modelling software. If you were in the world of SPSS, this would involve using Amos.
A: Factor analysis (which in SPSS will actually run a principal components analysis by default) is what you are after.   Or, if you want to test that your theoretical grouping is appropriate you can use confirmatory factor analysis (historically SPSS have marketed this as a part of their AMOS module, but I am not sure if they still do this).
Most of the more advanced market research texts will contain worked examples dealing with how to do this.
A: Perform Reliability test such as Cronbach's alpha. Also perform Factor Analysis and inter item correlation with deleted items. Many softwares are available for perform these test, SPSS is easy to used.
