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. 2020 Nov 4;32(1):371–450. doi: 10.1097/SCS.0000000000007035

TABLE 2. Level of Evidence for the Conclusion

Conclusion based on:
 1. Level A1 study or at least two mutually independent Level A2 studies
 2 .One Level A2 study or at least two mutually independent Level B studies
 3 .One Level B or C study
 4. Expert opinion