Table 5. Number of studies that clearly identified the experimental unit.

Species	Unclear†	No†	Yes†	No or Unclear (%)
Mouse (n = 16)	1	1	30	6
Primate (n = 16)	3	2	27	16
Rat (n = 16)	0	5	27	16
All (n = 48)	4	8	84	13*

^†In phase 2 of the survey all 48 studies were assessed independently by two assessors, therefore numbers in each row sum to twice the number of studies.

^*The experimental unit (e.g. a single animal or a group of animals) was not clearly identified in 13% (12/96) of the studies assessed.