Table 1 Confounding variables in the design and reporting of animal study protocols (list not exhaustive)

Ages of animals

Animals added to replace drop-outs

Bedding type/quantity

Blinding (i.e. blinding the investigators and staff to allocation)

Breeding

Cage position on shelving

Cage size/material

Circadian rythms

Cleaning (chemicals, methods and manual or automated cage washing)

Colony size

Co-morbidity

Dosing style and route

Enrichment methods and practices

Environmental (other)

Exercise (methods, equipment, timing, amount, locations)

Feeding (equipment, methods, timing, amount)

Feeds (type)

Frequency of intervention

Gender (male and/or female included)

Gender mix and family and community (ratios)

Genetic variation

Genotype

Handling

Husbandry techniques

Infection or infestation (not part of the research i.e. pin worm, fleas etc.)

Lighting

Litter size

Methods of analysis

Methods used to conceal allocation sequence

Methods used to generate allocation sequence

Model type (induced, spontaneous, transgenic, negative, orphan, or other)

Noise (background and foreground)

Nutritional deficiencies due to lack of normal living conditions

Odours (e.g. perfumes worn by technicians, laundry and cleaning products and medications)

Polypharmacy (whether accounted for to mimic target population - humans)

Randomisation of animals (details of methods used)

Recording methods (manual, electronic)

Research methods

Sample size estimation (whether computed and statistical method of computation)

Sampling of style and route

Sources of animals (e.g. same model may vary depending on supplier used)

Species

Staff changes and variation of routines

Staff numbers and attitudes

Statistics (full information on statistical methods used)

Strain

Substantiation (whether results substantiated under a range of conditions)

Surgical procedures

Temperature

Timing of induction of disease

Timing of intervention

Transportation methods

Unit of analysis

Water and watering methods

Weight of animals