Cronbach's alpha

As a measure of internal consistency, Cronbach's alpha assesses how reliably survey or test items that are designed to measure the same construct actually do so. Higher values of Cronbach's alpha suggest higher internal consistency. A historical benchmark value of 0.7 is commonly used to suggest that at least some of the items measure the same construct. However, benchmarks usually depend on the standards in your subject area and the number of items.  

For example, a bank manager wants to assess customer satisfaction. She asks customers to respond to the following three statements using a 5-point scale to indicate their level of agreement:

·    I was very satisfied with the service.

·    I am likely to buy from your company again.

·    I am likely to recommend your company to others.

If the Cronbach's alpha is high, then evidence exists that the items measure the same construct, customer satisfaction. On the other hand, if the value of alpha is low, then the items have little in common and are not good measures of the single construct.