> RNT was assessed using the perseverative thinking questionnaire (PTQ). The scale consists of 15 items covering three domains: core characteristics of RNT, unproductiveness, and psychological capacity captured. Each item is rated on a 5-point Likert scale from 0 “never” to 4 “almost always”, with a total score ranging from 0 to 60.

Can someone who works in this field explain to me how this study is anything other than evidence of one exam being a proxy for another?

The "Repetitive Negative Thinking" is then just, like, a marketing term for their questionnaire?

I don't see the questionnaire itself in the study (maybe I'm missing it?). Without understanding what questions were answered in a questionnaire, how am I supposed to take anything away from this study?