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. 2009 Sep 1;32(9):1155–1160. doi: 10.1093/sleep/32.9.1155

Table 2.

Circadian Rhythms Variables Derived from Actigraphy

Variables Definition Meaning

Amplitude The height of the rhythm. Value = maximum activity – minimum activity Lower amplitude suggests a dampened circadian rhythm.

Acrophase (h) Time of day of the peak of the curve A later time suggest more phase delay.

Mesor The mean of the rhythm; Value = Minimum + 1/2 amplitude Half-way between minimum and maximum activity Mean activity level

Up-Mesor (h) The time of day when the women switched from low activity to high activity, i.e., from below the mesor to above the mesor Higher value suggests a later starting time of activity; the time the women “got going” in the morning.

Down-Mesor (h) The time of day when the women switched from high activity to low activity, i.e., from above the mesor to below the mesor Higher value suggests a later time of decline of activity; the time the women “settled down” for the evening.

R-Squared The reduction in squared error from using a model to summarize data (and predict future values) compared to using the mean Higher value suggests a more rhythmic or robust rhythm.