I cannot seem to find in the MOP or published materials how the denominator for the state shifts (S→W or N3→N2/N1) are defined. Is it # of hours of TIB, recording hours, sleep onset → sleep offset, or something else? Just not sure what "hours of sleep" means...
Do you mean variables like the following? https://sleepdata.org/datasets/shhs/variables?search=shift
I opened the dataset and it looks like hstg2t1p is equal to stg2t1p/(time_bed/60), so it looks like time in bed is the denominator.