Stratification implies layers or differences. A quick test for soil composition is to place a sample of soil with water in a clear jar and give it a shake. The sand, silt and loam will settle at different rates and create a layered appearance within the jar over time. The height of each layer provides information about the proportion of each type of soil within the sample.

Stratification as one of the seven basic quality tools (some lists use a run chart or flowchart instead) the idea of layers or differences still applies. The idea is to identify potentially meaning differences within a sample set. [Read more…]

As reliability professionals, we are in the business of estimating or forecasting the reliability performance of our product, equipment, or system. While we use a range of tools to analytically make these estimates, sometimes we do not have sufficient data or information.

One method is to ask another person that has knowledge of the particular technology, use conditions, or whatever is hampering our work. If you ask two people you most like will get two different answers. If you ask 10, 10 different answers.

One way to work with a group of subject matter experts is to conduct a structured communication technique called the Delphi Method. [Read more…]

There are two common uses for a check sheet. First, to summarize historical data, or second, to collect observations. A byproduct of creating a check sheet is team agreement on definitions of categories and observation procedures.

The investment is minimal other than thinking about how you want to view the data, and what data to collect. [Read more…]

Reliability testing and data collection is a messy business.

We rarely receive perfect data where all units involved have a precise time to failure record. Sometimes we do not the precise time to failure information or some of the units are still operating.

The data is censored.

There are a few common types of censoring, each of which has statistical techniques to appropriately account for the unknown elements. [Read more…]