1. Study design The groups being compared, including control groups. If no control group has been used, the rationale should be stated. explanation

The choice of control or comparator group is dependent on the experimental objective. Negative controls are used to determine if a difference between groups is caused by the intervention (e.g. wild-type animals vs genetically modified animals, placebo vs active treatment, sham surgery vs. surgical intervention). Positive controls can be used to support the interpretation of negative results or determine if an expected effect is detectable.  It may not be necessary to include a separate control with no active treatment if, for example, the experiment aims to compare a treatment administered by different methods (e.g. intraperitoneal administration vs. oral gavage), or animals that are used as their own control in a longitudinal study. A pilot study, such as one designed to test the feasibility of a procedure might also not require a control group.

For complex study designs, a visual representation is more easily interpreted than a text description, so a timeline diagram or flow chart is recommended. Diagrams facilitate the identification of which treatments and procedures were applied to specific animals or groups of animals, and at what point in the study these were performed. They also help to communicate complex design features such as whether factors are crossed or nested (hierarchical/multi-level designs), blocking (to reduce unwanted variation, see item 4 – Randomisation), or repeated measurements over time on the same experimental unit (repeated measures designs), see [1-3] for more information on different design types. The Experimental Design Assistant (EDA) is a platform to support researchers in the design of in vivo experiments, it can be used to generate diagrams to represent any type of experimental design [4].

For each experiment performed, clearly report all groups used. Selectively excluding some experimental groups (for example because the data are inconsistent, or conflict with the narrative of the paper) is misleading and should be avoided [5]. Ensure that test groups, comparators and controls (negative or positive) can be identified easily. State clearly if the same control group was used for multiple experiments, or if no control group was used. 

References

1. Festing MF and Altman DG (2002). Guidelines for the design and statistical analysis of experiments using laboratory animals. ILAR journal. http://www.ncbi.nlm.nih.gov/pubmed/12391400
2. Bate ST and Clark RA (2014). The design and statistical analysis of animal experiments. Cambridge University Press. https://www.cambridge.org/core/books/design-and-statistical-analysis-of-animal-experiments/BDD758F3C49CF5BEB160A9C54ED48706
3. Ruxton G and Colegrave N (2017). Experimental design for the life sciences. Fourth Edition. Oxford University Press. https://global.oup.com/academic/product/experimental-design-for-the-life-sciences-9780198717355?cc=us&lang=en&
4. Percie du Sert N, Bamsey I, Bate ST, Berdoy M, Clark RA, Cuthill I, Fry D, Karp NA, Macleod M, Moon L, Stanford SC and Lings B (2017). The Experimental Design Assistant. PLoS Biol. doi: 10.1371/journal.pbio.2003779
5. The BMJ Scientific misconduct. (Access Date: 10 january 2020). Available at: https://www.bmj.com/about-bmj/resources-authors/forms-policies-and-checklists/scientific-misconduct