Sleep Fragmentation is an index of restlessness during the sleep period expressed as a percentage. Kristen L et al. 2011 (PubMed ID:21411507)
There are three type of measures for sleep fragmentation: movement Index (MI), fragmentation index (FI), and total sleep fragmentation Index. The fragmentation index refers to the percentage of 60s periods of sleep out of the total number of periods of immobility. The movement index refers to the total of scored awake minutes divided by sleep period (i.e. total time in bed). The total sleep fragmentation index is the sum of FI and MI. (ActiGraph validation reference)[https://actigraphcorp.force.com/support/s/article/Sleep-Fragmentation-Index-Validation-Reference]
This variable is similar to variable sawa26; however, sawa26 is generated by Actiware software before data optimization.