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 |