'weight20' was collected at the SHHS1 clinic visit, which corresponds with the initial round of home sleep testing. Weight was collected on a form alongside blood pressure and neck circumference at this clinic visit.
Sorry, I meant to ask if 'weight20' (https://sleepdata.org/datasets/shhs/variables/weight20) was measured before or after 'weight' (https://sleepdata.org/datasets/shhs/variables/weight) in SHHS1.
They were both measured at SHHS1, what is the difference between the two?
Good question. SHHS is, at times, difficult to understand! I pored over the original documentation from the SHHS Coordinating Center and here's my take:
'weight20' was collected at the time of the blood pressure collection (clinic visit) that was specifically geared toward SHHS (i.e. not a regular visit for the parent cohort study).
'weight' was likely collected from a time period before 'weight20'. 'weight' is listed in the documentation as an "A-variable", which were not collected as part of the SHHS clinic visit, but were reported otherwise by the parent cohort. The A-variable, in this case, would be used to compute BMI in instances where 'weight20' was not available.
To conclude, it looks like 'weight20' would be the preferred weight variable to use for SHHS1 since it happened closest to the SHHS clinic visit. We don't know how much earlier 'weight' was collected because the corresponding 'weightdt' (date of weight data collection) was stripped out of the final dataset.
Thank you very much for chasing this up!! Much appreciated