Observed Decimal Reduction Time

Estimate a measured D value from positive viable counts and exposure time under log-linear death assumptions.

Description

A decimal reduction time is the exposure duration associated with one log₁₀ reduction under a log-linear death model.

A decimal reduction time is the exposure duration associated with one log₁₀ reduction under a log-linear death model. A measured decrease supports an observed estimate; a zero endpoint is censored evidence rather than a usable logarithm.^[1]

Estimate a measured D value from positive viable counts and exposure time under log-linear death assumptions.

When to use Observed Decimal Reduction Time

Use this tool to estimate a measured D value from positive viable counts and exposure time under log-linear death assumptions.

Prepare the sample, count, growth or assay measurements requested by this tool. Confirm units, sampling periods and reporting bases; supply independently established comparison criteria where requested.

How to use Observed Decimal Reduction Time and understand its results

Prepare the sample, count, growth or assay measurements requested by this tool. Confirm units, sampling periods and reporting bases; supply independently established comparison criteria where requested.
Enter initialViableCount, finalViableCount, elapsedMinutes using the field table and calculation rules, then run the tool.
Read observedLog10Reduction, decimalReductionMinutes. 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
initialViableCount	Initial viable count	number	Required
finalViableCount	Final viable count	number	Required
elapsedMinutes	Elapsed minutes	number	Required

Enter positive initial/final viable counts and positive elapsed minutes, with final strictly below initial. The tool returns the observed log reduction and minutes per decimal reduction. Zero, unchanged or increasing final counts are input errors.

logReduction=log10(initial)−log10(final); Dminutes=elapsed/logReduction

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

Output field	Meaning	Value type
observedLog10Reduction	Observed log 10 reduction	number
decimalReductionMinutes	Decimal reduction minutes	number

json

{
  "input": {
    "initialViableCount": 100000,
    "finalViableCount": 100,
    "elapsedMinutes": 6
  },
  "output": {
    "observedLog10Reduction": 3,
    "decimalReductionMinutes": 2
  }
}

Limitations and assumptions

This two-point estimate does not test log-linearity, model shoulders/tails or validate a kill process. Assay detection limits, uncertainty and experimental conditions must be considered separately.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Thermal F0 Profile Integral: Integrate a sampled thermal profile by trapezoidal lethality at supplied reference temperature and Z value; F0 alone does not validate sterilization. For a complementary task, use Bactericidal Survival Endpoint: Find the first dilution meeting a caller-defined bactericidal kill fraction based on survivor counts, rather than merely recording MBC.

References

Observed Decimal Reduction Time — tool.io

Similar or alternative tools

Thermal F0 Profile Integral
Integrate a sampled thermal profile by trapezoidal lethality at supplied reference temperature and Z value; F0 alone does not validate sterilization.
Bactericidal Survival Endpoint
Find the first dilution meeting a caller-defined bactericidal kill fraction based on survivor counts, rather than merely recording MBC.