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Observed Life Table (OLT)
A table listing the percent surviving (ie., observed life) of a common class of assets, as of a particular calendar year.

An OLT is used to derive the following types of analytical data to assist in making reasonable forecasts of the service lives of similar assets under a variety of different operating conditions:

OLTs are a form of longitudinal study and are used to support demonstrated effectiveness as a life prediction technique.

For example:
  • "How many SBS roofs, within a defined statistical population, are still surviving after 25 years in service?"
  • How many gas fired water heaters are still in service after 12 years?
  • The Iowa Study utilized OLTs to develop a set of 31 survivor curves for utility infrastructure assets.

    Observed life tables are more effective than service life tables in that they provide data to develop additional insight into the skewness of the probability distributions.
    The degree of skewness represents variability in the following factors:
    • Local exposure conditions
    • Global maxima versus local minima
    Excerpt from an Observed Life Table (OLT)
    Fig. Excerpt from an observed life table (OLT).

    Left-modal and right-modal curves relative to their modes and their means.
    Fig. Left-modal ("L") and right-modal ("R") curves derived from the data in an observed life table (OLT).

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