3. Inclusion and exclusion criteria Describe any criteria used for including or excluding animals (or experimental units) during the experiment, and data points during the analysis. Specify if these criteria were established a priori. If no criteria were set, state this explicitly. explanation

Inclusion and exclusion criteria define the eligibility or disqualification of animals and data once the study has commenced. To ensure scientific rigour, the criteria should be defined before the experiment starts and data are collected [1-4]. Inclusion criteria should not be confused with animal characteristics (see item 8 – Experimental animals) but can be related to these (e.g. body weights must be within a certain range for a particular procedure) or related to other study parameters (e.g. task performance has to exceed a given threshold). In studies where selected data are re-analysed for a different purpose, inclusion and exclusion criteria should describe how data were selected.

Exclusion criteria may result from technical or welfare issues such as complications anticipated during surgery, or circumstances where test procedures might be compromised (e.g. development of motor impairments that could affect behavioural measurements). Criteria for excluding samples or data include failure to meet quality control standards, such as insufficient sample volumes, unacceptable levels of contaminants, poor histological quality, etc. Similarly, how the researcher will define and handle data outliers during the analysis should also be decided before the experiment starts (see item 3b for guidance on responsible data cleaning).

Exclusion criteria may also reflect the ethical principles of a study in line with its humane endpoints (see item 16 – Animal care and monitoring). For example, in cancer studies an animal might be dropped from the study and euthanised before the predetermined time point if the size of a subcutaneous tumour exceeds a specific volume [5]. If losses are anticipated, these should be considered when determining the number of animals to include in the study (see item 2 – Sample size). While exclusion criteria and humane endpoints are typically included in the ethical review application, reporting the criteria used to exclude animals or data points in the manuscript helps readers with the interpretation of the data and provides crucial information to other researchers wanting to adopt the model.

Best practice is to include all a priori inclusion and exclusion/outlier criteria in a pre-registered protocol (see item 19 – Protocol registration). At the very least these criteria should be documented in a lab notebook and reported in manuscripts, explicitly stating that the criteria were defined before any data was collected.

References

1. Avey MT, Moher D, Sullivan KJ, Fergusson D, Griffin G, Grimshaw JM, Hutton B, Lalu MM, Macleod M, Marshall J, Mei SHJ, Rudnicki M, Stewart DJ, Turgeon AF, McIntyre L and Canadian Critical Care Translational Biology G (2016). The devil is in the details: incomplete reporting in preclinical animal research. PLoS ONE. doi: 10.1371/journal.pone.0166733
2. Vahidy F, Schäbitz W-R, Fisher M and Aronowski J (2016). Reporting standards for preclinical studies of stroke therapy. Stroke. doi: 10.1161/STROKEAHA.116.013643
3. Rice ASC, Morland R, Huang W, Currie GL, Sena ES and Macleod MR (2013). Transparency in the reporting of in vivo pre-clinical pain research: The relevance and implications of the ARRIVE (Animal Research: Reporting In Vivo Experiments) guidelines. Scandinavian Journal of Pain. doi: 10.1016/j.sjpain.2013.02.002
4. Salkind NJ (2010). Encyclopedia of research design. Sage. doi: 10.4135/9781412961288
5. Workman P, Aboagye EO, Balkwill F, Balmain A, Bruder G, Chaplin DJ, Double JA, Everitt J, Farningham DAH, Glennie MJ, Kelland LR, Robinson V, Stratford IJ, Tozer GM, Watson S, Wedge SR, Eccles SA and An ad hoc committee of the National Cancer Research I (2010). Guidelines for the welfare and use of animals in cancer research. British Journal Of Cancer. doi: 10.1038/sj.bjc.660564