Calculating Life of Paint systems

[ashish]

I am measuring reliability of different Paint systems based on the following data:
- Time since last painted
- Percentage (%) of the exterior surface failed

If the threshold for Failure is 10% (of the exterior surface) then is it better to use:
- degradation analysis with a critical degradation of 10%, OR
- Weibull analysis with everything over 10% classified as Failures and less than 10% as Suspensions

What's the difference (if any) between the two analysis methods ?

We are making the assumption that the inspectors have been calibrated to record failure % with some degree of consistency and that the cars have NOT been inspected since their last paint date.

[Pantelis]

Degradation analysis allows you to “extrapolate” a failure time from multiple measurements. In other words you have time to 1%, 3%, 5% etc. degradation and want to find out the time to 10%. You then use “Weibull analysis” on the extrapolated data. Now if you already have sufficient data points to 10% degradation then you are better off using standard Weibull analysis.