Threat Score Critical Success Index

Compute observed threat/critical-success score on event-union cases, deliberately excluding correct negatives; no no-event division or precipitation probabilistic verification.

Description

Critical Success Index evaluates the union of forecast or observed event cases.

Critical Success Index evaluates the union of forecast or observed event cases. Correct negatives do not enter that denominator.

Compute observed threat/critical-success score on event-union cases, deliberately excluding correct negatives; no no-event division or precipitation probabilistic verification.

When to use Threat Score Critical Success Index

Use this tool to compute observed threat/critical-success score on event-union cases, deliberately excluding correct negatives; no no-event division or precipitation probabilistic verification.

Prepare the sounding profile or forecast verification counts. Check pressure levels, wind conventions, units and any requested layer bounds.

How to use Threat Score Critical Success Index and understand its results

Prepare the sounding profile or forecast verification counts. Check pressure levels, wind conventions, units and any requested layer bounds.
Enter hits, misses, falseAlarms, correctNegatives using the field table and calculation rules, then run the tool.
Read criticalSuccessIndex, eventUnionCaseCount. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
hits	Hits	integer	Required
misses	Misses	integer	Required
falseAlarms	False alarms	integer	Required
correctNegatives	Correct negatives	integer	Required

Use nonnegative integer contingency counts with positive event-union total. Validate the complete table but return only CSI and event-union cases. All-correct-negatives input has no defined CSI and errors.^[1]

CSI = hits/(hits + misses + false alarms)

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
criticalSuccessIndex	Critical success index	number
eventUnionCaseCount	Event union case count	number

json

{
  "input": {
    "hits": 30,
    "misses": 10,
    "falseAlarms": 20,
    "correctNegatives": 40
  },
  "output": {
    "criticalSuccessIndex": 0.5,
    "eventUnionCaseCount": 60
  }
}

Limitations and assumptions

The score is not probabilistic verification and ignores correct-negative abundance.

Numbers and computed results must be finite; overflow produces an error. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Equitable Threat Score ETS: Compute observed binary ETS after marginal random-hit correction, retaining possible negative skill; unlike raw CSI or HSS, correct negatives change chance hits but not event union directly. For a complementary task, use False Alarm Ratio Precip Verification: Compute observed false alarms/(hits+false alarms), not false-positive rate over observed nonevents; no-event forecasts leave ratio undefined.

References

Threat Score Critical Success Index — tool.io

Similar or alternative tools

Equitable Threat Score ETS
Compute observed binary ETS after marginal random-hit correction, retaining possible negative skill; unlike raw CSI or HSS, correct negatives change chance hits but not event union directly.
False Alarm Ratio Precip Verification
Compute observed false alarms/(hits+false alarms), not false-positive rate over observed nonevents; no-event forecasts leave ratio undefined.