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Table 1 Levels of evidence and strength of recommendation modified after [25, 26].

From: Antimicrobial Treatmdent of "Complicated" Intra-Abdominal Infections and The New IDSA Guidelines - A Commentary and an Alternative European Approach According to Clinical Definitions

Level of evidence Explanation
1 Meta-analysis of randomized controlled trials, good quality randomized controlled trials or 'all or none' studies in which no treatment is not an option
2 'Low quality' randomized controlled trials (< 80% follow up), meta-analysis of good quality prospective 'cohort studies' or well designed controlled study without randomization
3 Good quality retrospective 'case-control'-studies or comparative studies
4 Consensus, usual practise, disease-oriented evidence, and/or expert opinion
Strength of recommendation Explanation
A Use of agent is recommended ("do it")
B Use of agent should be considered ("probably do it")
C Use of agent may be considered ("is not recommended")