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Iowa Curves

One of various deterioration models applied to the life cycle or assets.

The Iowa curves are survivor curves developed in a study at the University of Iowa in the 1950s comprised of a set of 31 standardized patterns of asset retirement dispersion organized into four broad classes, as follows: The curves were developed using statistics and observed life tables (OLT).


Purpose and Application of the Curves
Each curve represents a probability distribution and has a series of attributes. The curves are helpful in a variety of ways, including:


Attributes
Listed below are some of the attributes of each of the four classes of Iowa curves.


       Right-Modal Curves
       Left-Modal Curves
       Symmetrical Curves
Some of the key statistical elements of an asset survivor curve
Fig. Some of the key statistical elements of an asset survivor curve.



Left-modal and right-modal curves relative to their modes and their means.
Fig. Left-modal curves (shown in "blue") and right-modal curves (shown in "green) relative to their respective modes and their means.


Bell curve (in "red") with perfect symmetry compared to skewed curves.
Fig. Bell curve (in "red") with perfect symmetry compared to skewed curves.


Generic left-modal curve (with positive skewness).
Fig. Generic left-modal ("L") curve (with positive skewness) indicating a long right tail.


Example of the probability distribution along a left-modal ("L") curve (positive skewness).
Fig. Example of the probability distribution along a left-modal ("L") curve (positive skewness).


Right modal curves to order-1, order-2 and order-3.  Three performance classes along a right-modal survivor curve.
Fig. Right modal curves to order-1, order-2 and order-3 (left) and three performance classes along a right-modal survivor curve (right) .


I. Care is trying to connect the dots in order to reveal the patterns in the data that underpins his assets, including trends.
Fig. I. Care is trying to connect the dots to reveal the patterns in the data that underpin his assets.

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