A product may have many defects – imperfections. But a product is not defective unless the defects prevent the product from functioning.
A Scatter Analysis is used when you need to compare two data sets against each other to see if there is a relationship.
The T distribution and T tests are used to determine the likelihood of various conditions occurring for small sample sizes (<=30).
Value Stream Mapping is a material & information flow map. It’s also a tool for visualizing processes that need improvement.
A Cause and Effect Diagram (aka Ishikawa, Fishbone) showing possible causes (process inputs) for a given effect (process outputs).