This aim considers whether an appropriate number and species of animals have been selected for a particular experiment. Using too many animals must be avoided whilst using too few may result in an inconclusive result, necessitating wasteful repetition. Reducing the number of animals required involves careful experimental planning and good statistical analysis of data, including, for example, the use of pilot studies.
When calculating animal usage in experiments, it is important to take into account any animals which may have been produced but not used. This includes any additional animals that are inevitably generated when breeding experimental animals that cannot themselves be used in experiments because of their gender or genetic makeup. Minimising sources of variability such as genetic diversity, gender and age can reduce the number needed to generate clear data, although it is also essential to ask whether results obtained in this way have wider relevance, especially to the diverse human population.
As well as ensuring careful experimental planning, Reduction should also be an active process to look at ways in which established experimental designs can be improved with no loss of information quality.