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Table 4 Criteria used for critical appraisal: global sources of biases assessed for internal validity of studies included in our systematic review (I/E: Intervention/Exposure)

From: How effective are strategies to control the dissemination of antibiotic resistance in the environment? A systematic review

Bias Definition Solutions to limit the bias
Confounding bias Error of assessment in the association between I/E and outcome (a factor is independently associated with the I/E and the outcome) Presence of a control before and/or without I/E
Randomization (e.g., randomized allocation of animals in groups), stratification and statistical adjustment
Selection bias Difference of composition between control and I/E groups Same numbers of study objects in control and I/E groups
Similar baseline for I/E and control groups
Measures to avoid contamination between I/E and control groups
Performance bias Error of assessment between the effects of the I/E and the consequences of confounding variables Control of confounding variables that particularly contribute to the spatial and temporal heterogeneities, by repeating the measurement
Adaptation of the study duration (sufficiently long to see the effect of I/E)
Detection bias Difference between groups in how outcomes are determined
Error of assessment between the effects of I/E and the consequences of measurement errors
Representative sampling: composite samples
Same sampling times for comparison between I/E and control groups
Control of conditions to sample, transport and store samples to limit their degradation and external contamination
Analytical replication and control
Attrition bias Difference between initial and final groups (at the end of study), with respect to trial outflows, treatment interruptions, loss of samples No real solution; it would be appreciated if authors justify the potential attrition in the course of the study
Reporting bias Incomplete reporting of materials and methods or outcome results