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Table 4 Some underlying evidence for the importance of random housing and random outcome assessment

From: SYRCLE’s risk of bias tool for animal studies

Random housing
Lighting Light exposure varies with respect to rack location and position of cages within the rack [27, 28]
  Small differences in light intensity have been associated with reproductive and behavioral changes [27, 29, 30]
  There can be a four-fold difference in light intensity between cages at the top or bottom of a rack [18]
Temperature Temperature in animal room at 1.5 m can be 3-4˚C higher than at 0.5 m [18]
  Cage temperature varies with group size [18]
  Cage temperature varies with height of placement within the rack (top rack 5˚C warmer than bottom rack) [18, 31, 32]
  Small changes in temperature can influence metabolic rates and toxicity [27, 31, 33]
Random outcome assessment
Circadian rhythm Periodic/circadian variations in lipid metabolism, neurotransmitter levels, pharmacokinetic effects, etc. [3437]
  1. Suggestions for further reading: [18, 27, 37, 38].