3c. Numbers analysed

What to write

For each analysis, report the exact value of n in each experimental group.

Explanation

The exact number of experimental units analysed in each group (i.e., the n number) is essential information for the reader to interpret the analysis; it should be reported unambiguously. All animals and data used in the experiment should be accounted for in the data presented. Sometimes, for good reasons, animals may need to be excluded from a study (e.g., illness or mortality), or data points excluded from analyses (e.g., biologically implausible values). Reporting losses will help the reader to understand the experimental design process, replicate methods, and provide adequate tracking of animal numbers in a study, especially when sample size numbers in the analyses do not match the original group numbers.

For each outcome measure, indicate numbers clearly within the text or on figures and provide absolute numbers (e.g., 10/20, not 50%). For studies in which animals are measured at different time points, explicitly report the full description of which animals undergo measurement and when¹.

Examples

‘Group F contained 29 adult males and 58 adult females in 2010 (n = 87), and 32 adult males and 66 adult females in 2011 (n = 98). The increase in female numbers was due to maturation of juveniles to adults. Females belonged to three matrilines, and there were no major shifts in rank in the male hierarchy. Six mid to low ranking individuals died and were excluded from analyses, as were five mid-ranking males who emigrated from the group at the beginning of 2011’².

‘The proportion of test time that animals spent interacting with the handler (sniffed the gloved hand or tunnel, made paw contact, climbed on, or entered the handling tunnel) was measured from DVD recordings. This was then averaged across the two mice in each cage as they were tested together and their behaviour was not independent…. Mice handled with the home cage tunnel spent a much greater proportion of the test interacting with the handler (mean ± s.e.m., 39.8 ± 5.2 percent time of 60 s test, n = 8 cages) than those handled by tail (6.4 ± 2.0 percent time, n = 8 cages), while those handled by cupping showed intermediate levels of voluntary interaction (27.6 ± 7.1 percent time, n = 8 cages)’³.

Training

The UK EQUATOR Centre runs training on how to write using reporting guidelines.

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References

1.

Vahidy F, Schäbitz WR, Fisher M, Aronowski J. Reporting standards for preclinical studies of stroke therapy. Stroke. 2016;47(10):2435-2438. doi:10.1161/strokeaha.116.013643

2.

Brent LJN, Heilbronner SR, Horvath JE, et al. Genetic origins of social networks in rhesus macaques. Scientific Reports. 2013;3(1). doi:10.1038/srep01042

3.

Gouveia K, Hurst JL. Optimising reliability of mouse performance in behavioural testing: The major role of non-aversive handling. Scientific Reports. 2017;7(1). doi:10.1038/srep44999