How we measure your response: formulas, windows and limits

Three rules every number follows

It describes what happened in your data; it does not predict what will happen.
It comes with its context: how many times it was seen (n), in what range and with what confidence.
It speaks of associations (“after X came Y”), never of causes: food, exercise, insulin, medication, sleep, time of day and stress all act on your glucose at once.

Period statistics

They are calculated over all readings in the chosen period, weighted by the time each one covers (at most 20 minutes, so that a sensor gap does not count as if there were data).

Time in range (TIR): Percentage of time with glucose inside your target range. We show it with your range (the one you set in Settings) and also with the international standard of 70–180 mg/dL, so you can compare it with what your care team uses.
Time below and above (TBR, TAR): Percentage below the bottom of your range (and, separately, below 54 mg/dL) and above the top (and, separately, above 250 mg/dL).
Mean and variability (CV): Weighted mean of the period and coefficient of variation: standard deviation divided by the mean, as a percentage. The lower, the steadier.
GMI: Glucose management indicator: 3.31 + 0.02392 × mean in mg/dL (Bergenstal et al., 2018). It is an estimate from the mean and does not replace a lab HbA1c.
Episodes: A stretch counts as an episode (low or high) when glucose stays out of range for at least 15 minutes in a row, with no gaps longer than 30 minutes between readings.
Coverage: Fraction of the period with sensor data. When it is low, the period's figures are worth less and we tell you.

Ambulatory glucose profile (AGP)

It is the standardised format used by sensor reports: every day of the period overlaid on a single 24-hour day.

How it is built: Readings are grouped into 15-minute slots by local time and each slot is smoothed with its two neighbours on each side (±30 minutes). For each slot we draw the 5th, 25th, 50th (median), 75th and 95th percentiles.
When it is not drawn: A slot with fewer than 5 readings stays empty: we do not invent the curve.

Response to an event

Every meal, workout, dose, medication or sleep you log is an event. GlucoBeat looks at your curve over the following hours and describes what happened.

Starting level: Median of the readings in the 30 minutes before the event. If there are none, the value interpolated at that moment (only if there are readings less than 30 minutes away on each side).
Window we look at: It depends on the type: meal 3 h, exercise 4 h (or the length of the session if you logged it, then what happened after it ended), insulin 4 h, medication 4 h, treating a low 90 min, sleep 8 h, waking up 3 h.
Rise, peak and time to peak: Difference between the highest value in the window and the starting level, and minutes until that maximum. The same with the minimum (drop) for exercise and insulin.
Return to the starting level: Minutes until the first reading, after the peak, that is within 10 mg/dL of the starting level. Only calculated if the peak rose more than 20 mg/dL above that level.
Out of range: Whether any point in the window went above or below your range.
Overlapping events: If there is another meal, workout, dose or treatment of a low between 60 minutes before and 120 minutes after, the response is flagged as “other events nearby”: what happened cannot be attributed to that one alone.
When it is not shown: If the sensor covers less than half of the window, there is no response to measure and no figure is shown.

Usual response and similar meals

When you have logged the same meal several times, or similar meals, we pool their responses so you can see what repeats.

Which meals are pooled: Those with the same normalised text (no capitals or accents) and, for “similar meals”, those sharing meaningful words with what you type, compared by trigrams and by words in common. Stop words (“with”, “of”, “plate”…) are discarded.
What is calculated: How many times (n), the median rise, the usual range (25th and 75th percentiles), the usual time to peak, the return to the starting level and what fraction went out of range. And, when there are enough, the same comparison splitting the times with exercise in the next 2 hours from the times without it.
Minimums: At least 2 measurable responses are needed (with starting level, peak and enough coverage). With fewer, nothing is shown.

Confidence

Each aggregate carries a confidence label that comes from three things: how many observations there are, how many are clean (no other events nearby) and how much sensor coverage there was.

High: 5 or more observations and at least 60% clean.
Medium: 3 or 4 observations.
Low: 2 observations. A hint, not a pattern.
The AI's: In AI results, confidence is declared by the model itself according to the data it received, and it is shown as is, together with whether it relied on your history, on general knowledge or on both.

What the AI does and what it receives

The AI does not see your raw data and does not decide anything for you. It only comes in when you ask, and it receives a pseudonymised summary: no name, email or identifiers, with dates as relative days and times.

Period analysis: It receives the statistics, the 24-hour profile, and each event with its measured response as explained above. It is asked to describe associations in your data (“in your data, X was followed by Y, n times”), to state confidence and data quality, and never to talk about causes, doses or diagnoses.
“How would this affect me?”: First you see your usual response, calculated without AI. Then the AI receives that same usual response, your recent and similar meals with their responses, your glucose over the last 3 hours and what you have done in the last 4, and returns an estimate with a range, labelled as an estimate, with its confidence and its basis. Never a permission verdict or an exact figure.
Guardrails: After the answer is generated, a filter removes any sentence with dose amounts, treatment adjustments or diagnoses, and tells you it was removed.

What we do not do

We do not predict or forecast: the figures describe your past and the estimates come with a range and a label.
There is no clinical validation of these calculations as a medical tool: they are descriptive and indicative, to understand your data and arrive at your appointment well informed.
We do not raise alarms or alerts on glucose values, and we do not work in real time: your sensor and its app do that.
We do not give doses, ratios or treatment adjustments, nor diagnoses. Ever.
We do not claim causes: what we see are associations in your data, which may be due to many things at once.

References

Check it with your own data

Every figure you see in GlucoBeat can be traced back to this page. If something does not add up, write to us.

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