Total time on test plot for Parametric Growth Curve

Use a total time on test (TTT) plot to visualize how well your model fits the data.

The TTT plot provides a way to assess goodness-of-fit for the power-law process.

  • If the points on the TTT plot are close to the diagonal (45°) line, then a power-law process or a homogeneous Poisson process model is appropriate. Because the points follow the line, the system is stable.
  • If the TTT plot is a curve that is either concave up or concave down, then a power-law process is appropriate. If the curve is concave down, then the system is deteriorating. If the curve is concave up, then the system is improving.
  • If the plot shows no pattern, or a curve that alternates between concave up and concave down, then neither the homogeneous Poisson process nor the power-law process is adequate.

Example Output


For the air conditioning data, the points on the TTT plot are close to the 45° line, which indicates that the power-law process or homogeneous Poisson process provides an adequate fit for the data.

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