Degree to which rest and activity break into many short bouts within a day, quantified as intradaily variability (IV).
Use intradaily variability when the question is whether the rest-activity pattern is consolidated or broken into many short bouts. IV rises with fragmentation and is a sensitive marker in aging and neurodegeneration, often changing before period does. It complements amplitude rather than replacing it.
| Primary value | Intradaily variability (IV): ratio of hour-to-hour variance to overall variance |
|---|---|
| Common units | Dimensionless index, roughly 0 (consolidated) to 2 (fragmented) |
| Compatible assays | Home-cage video, beam-break, actigraphy |
| Required boundary | Bin size and number of days |
| Do not infer alone | Period, phase, or amplitude |
Compute IV as the ratio of the mean squared difference between successive time bins to the overall variance of the activity record. Higher values mean more frequent transitions between rest and activity. Bin size strongly affects the value, so keep it fixed across groups.
High IV indicates a fragmented pattern but does not localize the cause; sleep disruption, motor restlessness, environmental disturbance, and clock dysfunction all raise it. Interpret IV together with interdaily stability and amplitude.
Store animal ID, bin size, days analyzed, IV value, and activity measure.
Endpoint pages should cite the method literature behind the scored value and keep high-specificity protocol claims qualified unless the source supports them.
Endpoint articles link to adjacent products, software workflows, and sibling endpoints where the connection is useful and already routable.
