The State Index: Today vs Your Personal 28-Day Baseline

The formula

z = (x_d − median_baseline) / (1.4826 · MAD_baseline)
SI_d = mean(z_{Plane I}, z_{Plane II})

Plane I combines nightly lnRMSSD, sleep duration and the size of the deviation in sleep midpoint. Plane II uses the daily mean of positive minus negative affect from experience sampling.

Defaults

State Index defaults
Parameter	Default
Baseline	28 days rolling, at least 14 valid days
Plane weights	Equal
Robust scaling	Median and MAD × 1.4826, consistent with the standard deviation under normality
Output	Daily value, components and valid-day count

Why robust scaling

The median and the median absolute deviation (MAD) are less affected by a single unusual night than the mean and standard deviation, so the baseline stays stable.

Questions

Is a low State Index bad?

It means today differs from the person's recent normal. It is descriptive, and it is never presented as a health judgment.

Keep reading

Resilience (recovery half-life)How ATS-1 measures resilience as recovery speed: an AR(1) model of nightly HRV gives a recovery rate λ = −ln φ and a half-life t½ = ln 2 / λ over 60 days.Plane methodsHow ATS-1 collects each plane: nightly lnRMSSD, sleep timing, provenance, IEEE 1752.1 mapping, WHO-5 every 14 days and sampling rules.HRV and recovery explainedWhat heart-rate variability is, why nightly lnRMSSD against your own 28-day baseline beats daytime spot readings, and how recovery speed is measured.The five indicesThe five ATS-1 indices: State Index, Resilience, State-Change Signal, Coherence and Metabolic Balance, what each describes and how each is reported.

Take the next step.

The ATS-1 State Index: robust z-scores of HRV, sleep and affect against a 28-day personal baseline, using the median and MAD. Formula and defaults.

Get the textbook Resilience