Most quality professionals are familiar with basic hypothesis tests such as the 2-sample t test.  However, depending on the goals of the study, another type of test, called an equivalence test, may be utilized instead of traditional hypothesis tests.  This article will review statistical hypothesis testing in general and then introduce equivalence testing and its application.  To illustrate the differences between traditional hypothesis tests and equivalence tests, we will focus on the case of comparing 2 independent samples.  The concepts may be easily extended to other situations (such a comparing a sample to a target or paired comparisons).   [Read more…]

SPC and Reliability

We often think of Statistical Process Control as a tool to help drive product quality by informing us when process changes occur.  By systematically detecting (and rectifying) sources of special cause variation upstream in the process, the important process outcomes become predictable.  Furthermore, a focus on reducing common cause variation drives higher levels of process capability and more consistent product performance. [Read more…]

In order to maximize profitability while complying with government regulations regarding net package contents, food manufacturers and packagers must achieve an optimal balance.  Consistent overfilling to minimize risk is inefficient and sacrifices profitability, while aggressive filling practices result in significant risks of non-compliance with net contents regulations leading to potential penalties, loss of reputation, and impaired customer relations.  Statistical process control and process capability methods may be utilized to determine optimal targets for product fill weights or volumes for a given process.  Subsequent focused efforts to minimize variation will allow the target to be further optimized, resulting in less waste without compromising risk. [Read more…]