Other illnesses including heart disease, Alzheimer's disease and hormonal problems can also disturb the normal pattern of sleep.

BBC: High sleeping pill use 'worrying'

Algorithms might be designed, for example, to infer how many times per day a refrigerator door was opened (relevant to dietary and obesity studies), the times of day a residence was occupied (relevant to air pollution health studies), and even the pattern of sleep (relevant to a variety of health studies).

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