I need to understand what a repeatability coefficient is. I know it is some sort of measurement for test-retest reliability, but I need to know how the value is calculated, and how you determine if...

I need to understand what a repeatability coefficient is. I know it is some sort of measurement for test-retest reliability, but I need to know how the value is calculated, and how you determine if the value calculated is significant. I am evaluating a research article and it reports a repeatability coefficient. , The study, "Development of a self-reported Chronic Respiratory Questionnaire (CRQ)" by Williams et al., 2001, in the journal "Thorax", is in the Medline database. The authors state that their findings indicate a high test-retest reliability, but I don't know what the standard is that they compare it to, to determine that. For example if a researcher reports a Cronbach's alpha of 0.83, I know that indicates a strong internal consistency because it is greater than 0.7. I need to understand the repeatability coefficient in the same way.