A colleague and I are independently working on a scoping review on effectiveness of a physiotherapy intervention. One question of the review is what is the spectrum of current levels and quality of research on the intervention and each sub-application. Articles included from our search are of mixed types ranging from case series to systematic reviews. Is there an appropriate or best standardized tool for simply rating the quality (i.e. high, medium, low) of such variety of articles?
I've considered GRADE and MMAT already but to my novice eyes they don't seem quite the right fit.