Use when
- Testing happens across different times of day or across multiple rooms.
- The endpoint depends on activity, exploration, feeding, sleep, or arousal.
- The study compares cohorts tested on different schedules.
Experimental Confounds
Experimental confound
Circadian phase
Circadian phase affects physiology, movement, arousal, and task engagement, so test timing should be planned and reported.
Decision summary
Control circadian phase when endpoints depend on activity, sleep, metabolism, arousal, or learning. Report time of day relative to the light cycle, not only the clock time.
| Timing variable | Zeitgeber time or time relative to lights on/off. |
|---|---|
| Affected endpoints | Distance, latency, preference, feeding, sleep, and physiological readouts. |
| Control action | Balance groups across time blocks or keep testing windows fixed. |
| Audit field | Room light cycle, session time, and order by group. |
Do not use when
- Groups were tested in different light-cycle windows without balancing.
- The light cycle or testing time is missing from the method record.
Caveats
- Clock time alone is insufficient when rooms have different light schedules.
- Testing order can confound group with circadian phase.
- Phase effects can interact with lighting, feeding, and handling.
Reporting checklist
- Report light/dark cycle and testing window.
- State time relative to lights on or lights off.
- Report whether groups were balanced across time blocks.
- Report deviations from the planned testing window.
- State whether acclimation matched the testing schedule.
References
Nelson and Takahashi 1991. Comparison of visual sensitivity for suppression of pineal melatonin and circadian phase-shifting.
Circadian context for light sensitivity and phase effects.
https://pubmed.ncbi.nlm.nih.gov/1837583/
ARRIVE 2.0 guidelines 2020.
Reporting framework for timing and environmental context.
https://pubmed.ncbi.nlm.nih.gov/32663219/
Related surfaces
Use these related surfaces to move from the scientific method question to the relevant product page, endpoint definition, analysis tool, or adjacent guide.
