I have found a variable 'StOnsetP' in SHHS. It's described as "Sleep onset time" and united as time. However, it has a numerical value instead of a time. This confused me. Who can kindly explain the meaning of its value and its correlation with the variable 'slplatp' (Sleep Latency, unit: min) for me?
Thanks a lot.
Thanks for the inquiry. I can see how this would be confusing, so I apologize for that. I will make a note to update our data dictionary definitions in a future release.
STONSETP actually has different meanings in the 'shhs1' and 'shhs2' datasets. It is a clock time in the 'shhs2' dataset (as you expected), however in 'shhs1' it actually represents the "number of 30-second epochs from the start of the recording to sleep onset". This applies to STLOUTP as well. The PSG scoring software and its output style changed between SHHS1 and SHHS2.
SLPLATP represents the time (in minutes) between "lights out" and "sleep onset". If "lights out" was at 22:00:00 and sleep onset was at 22:30:00 then SLPLATP would be 30 minutes. This bit of documentation about the PSG scoring has more information about sleep latency.
Thank you very much for your quickly reply.
So in SHHS1, does the edf data start to be recorded before (at least not later ) than the light out? There is a latency between the start of recording to light out? Is there a variable representing for this ?
Most EDFs follow this pattern:
With "..." representing some passage of time (be it 5 minutes, 15 minutes, etc.) However, if "lights off" could not be detected it will be marked at the same epoch as "sleep onset", which makes the "sleep latency" equal zero (0) minutes. This is described in the documentation page I linked in my previous post. A small subset of studies actually began in sleep, in which case recording start, lights off, and sleep onset should be simultaneous. These SHHS1 studies are indicated by the RESTAN2 variable.
Thanks. I got it.
Another question, is there any variable to represent the sleep-restorability in the morning?
What do you mean by "sleep-restorability"? Something like "sleep quality"? Oftentimes sleep efficiency (SLP_EFF) is used as a measure for how well someone slept over the night. A higher sleep efficiency typically indicates you are waking up less during the night and that your sleep is more continuous (not fragmented).
I want to find a measure to judge the sleep quality such as is it a restorative sleep or not?
There are two variables for sleep efficiency, SLP_EFF and SLPEFFP. Would you please figure out the difference of them for me? Sometimes, there is no SLP_EFF available but SLPEFFP always has a value.
Moreover, for some subjects, the time durations recorded by SPonsetP are much larger than Slplatp. I wonder what's the state for those subjects, resting with eye closed in bed or active not in bed?
My best guess is that SLP_EFF was filtered in SHHS1 to only use cases where the lights off/on and sleep onset data were reliable. SLPEFFP clearly contains impossible values (>100) in SHHS1.
In SHHS1, STONSETP represents the number of epochs from the beginning of the recording until the marking of sleep onset. SLPLATP is the number of minutes between lights off and sleep onset. Having a "STONSETP much larger than SLPLATP" might simply mean that the device was recording a lot of time before the participant got into bed (lights off). If SLPLATP is large this would mean the participant was lying in bed for a long time but not sleeping.
Is there any variable about the percentage of deep sleep?
Yes, there are many variables that describe sleep architecture.
TIMES34P is the "percent of sleep time in stage 3-4 sleep" (deep sleep).
Thanks for your reply.
Still a question about TIMES34P. Is it calculated by （Time in stage 3-4 sleep）/( total sleep time) ? The denominator is the time excluding all period of wake?
Yes, that is correct.