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General Examples Using the Gompertz Models |
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Sometimes reliability growth data with an S-shaped trend cannot be described accurately by the Gompertz or Logistic curves. Since these two models have fixed values of reliability at the inflection points, only a few reliability growth data sets following an S-shaped reliability growth curve can be fitted to them. A modification of the Gompertz curve, which overcomes this shortcoming, is given next [5].
If we apply a shift in the vertical coordinate, then the Gompertz model is defined by:
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where:
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The Modified Gompertz model is more flexible than the original, especially when fitting growth data with S-shaped trends.
Note that this discussion describes the application of the model for the Reliability data type but the Modified Gompertz model also can be applied for discrete (success/failure) data. For more information, refer to Using the Gompertz Model for Discrete Data.