Fig 5. Acrophase ϕ₀(t) as a function of time.

Results for the subjects of Fig 1. Within the cosinor approach (dashed lines), the deviation from the ideal 24h circadian cycle is small for the control subject, ΔT = +3min, such that ϕ₀(t) is rather constant (blue dashed line), whereas for the subject with acute insomnia the circadian deviation is larger, ΔT = −24min, and ϕ₀(t) is a downsloping linear function (red dashed line). SSA (continuous lines) allows to calculate the day-to-day variability of acrophase ϕ₀(t), and are found to fluctuate around the average behaviour obtained within the cosinor approach.