4. Randomisation Describe the strategy used to minimise potential confounders such as the order of treatments and measurements, or animal/cage location. If confounders were not controlled, state this explicitly. explanation

Ensuring there is no systematic difference between animals in different groups apart from the experimental exposure is an important principle throughout the conduct of the experiment. Identifying nuisance variables (sources of variability or conditions that could potentially bias results) and managing them in the design and analysis increases the sensitivity of the experiment. For example, rodents in cages at the top of the rack may be exposed to higher light levels, which can affect stress [1].

Reporting the strategies implemented to minimise potential differences that arise between treatment groups during the course of the experiment, enables others to assess the internal validity. Strategies to report include: standardising (keeping conditions the same, e.g. all surgeries done by the same surgeon), randomising (e.g. the sampling or measurement order), blocking or counterbalancing (e.g. position of animal cages or tanks on the rack), to ensure groups are similarly affected by a source of variability. In some cases, practical constraints prevent some nuisance variables from being randomised, but they can still be accounted for in the analysis (see item 7 – Statistical methods).

Report the methods used to minimise confounding factors alongside the methods used to allocate animals to groups. If no measures were used to minimise confounders (e.g. treatment order, measurement order, cage or tank position on a rack), explicitly state this and explain why.

References

1. Ishida A, Mutoh T, Ueyama T, Bando H, Masubuchi S, Nakahara D, Tsujimoto G and Okamura H (2005). Light activates the adrenal gland: timing of gene expression and glucocorticoid release. Cell Metab. doi:10.1016/j.cmet.2005.09.009