“…Several studies used an existing tool, like the STate Action on Avoidable Rehospitalizations (STAAR) initiative [14, 21, 27, 30, 34] or root cause approach [5, 18, 24, 35–37] but all others adapted an existing tool or developed their own tool based on previous publications. For the purpose of this article we focused only on the distinction between studies using an a priori preventability cause classification [13–16, 19, 21–26, 31, 35, 37–55], or not [5, 17, 18, 20, 27–30, 32, 33, 36, 56–59], see Table 2 . As an example of an a priori cause classification, Clarke et al reported, Unavoidable causes: chronic or relapsing disorder; unavoidable complication, readmission for social or psychological reason, reasons probably beyond control of hospital services, completely different diagnosis from previous admission.…”