This page provides more detailed information on the statistical models used in InfoAsset Planner's Deterioration Models.

# Cohort Model: Weibull

**Data Inputs**: User-defined life expectancies (per Cohort), or failure Data.

**Processes:** Estimates input parameters (typically referred to as the shaping factors) for the Weibull distribution and then calculates the probability (for a given Cohort) as a function of time.

#### Distribution Function:

**Where:**

*f*(*t*) is pipe failure probability density function (pdf);

*t* is the pipe age;

k is the shape parameter;

λ is the scale parameter;

c is the resistance time or the elapsed time from the construction to the first observed failure (*t* > *c*).

**Outputs:** Failure Probability Density, Cumulative Failure Probability, Survival Probability, Residual Life Expectancy

**Comments:** Network and Cohort level analysis, more general failure equation designed for deterioration analysis for many different applications, easier to converge and generally requires less data