Table 2.

Minimum and optimal recommendations for consideration of sex as a variable in animal studies

Minimum	Optimal
Study design, data collection, and data analysis
• Power analysis to determine feasibility of including both sexes. • Consider level of evaluation (molecular, cellular, organ, and whole animal). • Animal housing (e.g., cage conditions, group/single housing). • Breeding status or history (i.e., virgin, bred, or retired breeders). • Collect primary outcomes for both sexes.	Minimum, plus: • Sample size sufficient for analysis within and between sexes. • Match animals for breeding history. • Estrus cycle and/or hormone levels. • Collect and analyze secondary outcomes for both sexes. • Analyze data within and between sexes.
Reporting
• Report a priori power analysis results if primary focus is on sex differences. • Present collective results as well as data from each sex individually. • Include general breeding history of animals. • Effects unique and common to sexes (similarities are as important as differences).	Minimum, plus: • Statistical analysis of collective and sex-specific data for comparison between sexes. • Report sex hormone concentrations or estrus cycle information.
Data interpretation
• Distinguish statistical vs. biological differences. • Include limitations (e.g., sample size, confounding variables like breeding history). • Keep focus within the context of your sample set.	Minimum, plus: • Include interpretation of data based on estrus phase and sex hormone levels as applicable.