Parametric Growth Curve Models
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The first step in the analysis of a repairable system is to check for a trend in the rate of failures or repairs. Minitab provides two types of models for estimating parametric growth curves:

·    Power-law process - Use to model failure/repair times that have an increasing, decreasing, or constant rate. The repair rate for a power-law process is a function of time.

With the default maximum likelihood estimation method, the power-law model is also referred to as the AMSAA model. With the least squares estimation method, the power-law model estimation method is also known as the Duane model.

·    Poisson process - Use to model failure/repair times that remain stable over time.

Choose your model based on whether or not a trend exists in the failure/repair rate.