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Reliability and Survival Methods > Repeated Measures Degradation > Statistical Details for the Repeated Measures Degradation Platform
Publication date: 06/21/2023

Statistical Details for the Repeated Measures Degradation Platform

The repeated measures degradation model can be expressed as follows:

Equation shown here

where:

h is the transformation for the Y variable

g is the transformation for the time variable

μ is a function of the parameter vector θ, the time t, and the option explanatory variable X

θ is a vector of parameters

i indicates the unit ID

t indicates the timestamp of the measurement

X is an optional explanatory variable

the error term εit are independent and identically distributed as N( 0, σε ).

Note: Some of the θ parameters are fixed, such that they are unknown but do not vary from unit to unit. Other parameters in θ are random parameters, such that they vary from unit to unit. The random parameters can follow a normal or lognormal distribution.

The residuals are computed on the transformed Y scale: h(Y) - μ.

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