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Alert Threshold (Moving Average) Calculator

Work out alert threshold (moving average) instantly with clear inputs, formula shown and shareable results.

About Alert Threshold (Moving Average) Calculator

Builds an aberration detection threshold from a moving average plus a sigma multiple, the basis of the Early Aberration Reporting System C-charts.

Formula

Moving average threshold

Threshold = moving average + k x standard deviation of the baseline window; a signal is raised when the current count exceeds it

Worked example

With the default values below, Alert Threshold (Moving Average) Calculator returns Moving average alert threshold of 23.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Moving average of recent periodsaccepts 0.1–100,000
15
Standard deviation of the baselineaccepts 0.01–10,000
4
Current period countaccepts 0–1,000,000
24
Sigma multiplieraccepts 1–5
2

Results

Moving average alert threshold
23.000 cases
Signal status
Signal — count exceeds the moving average threshold
Observed to expected ratio
1.600
Standard deviations above the moving average
2.250

Step by step

  1. 1Values used
  2. 2Moving average threshold
  3. 3Moving average alert threshold= 23.000 cases
  4. 4Signal status= Signal — count exceeds the moving average threshold
  5. 5Observed to expected ratio= 1.600
  6. 6Standard deviations above the moving average= 2.250

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How long should the baseline window be?

Seven periods is the CDC C1 default, with a guard band before the current period to avoid contaminating the baseline.

Why use a guard band?

If the outbreak has already begun, including recent periods in the baseline raises the threshold and hides the signal.

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