8.
Assessing Product Reliability
8.4. Reliability Data Analysis


Graphical estimation methods (aided by computer line fits) are easy
and quick
Maximum likelihood methods are usually more precise  but require special software 
Two widely used general methods will be described in this section:
Recommendation On Which Method to Use
Maximum likelihood estimation (except when the failure data are very sparse  i.e., only a few failures) is a more precise and flexible method. However, with censored data, the method of maximum likelihood estimation requires special computer programs for distributions other than the exponential. This is no longer an obstacle since, in recent years, many statistical software packages have added reliability platforms that will calculate MLE's and most of these packages will estimate acceleration model parameters and give confidence bounds as well. If important business decisions are based on reliability projections made from life test data and acceleration modeling, then it pays to obtain stateofthe art MLE reliability software. Otherwise, for monitoring and tracking reliability, estimation methods based on computeraugmented graphical procedures will often suffice. 