Observed performance

The number of units in your process output that violate the specification limits. This statistic is based on combined data from all subgroups, so it represents what your customer experiences. The observed performance can be expressed in terms of nonconforming parts per million (PPM) or per hundred (percent).

For example, a dairy farm fills 1 gallon milk cartons and you are analyzing the capability of the filling machine. The manager demands a maximum PPM defective of 1900. You produce the following table of observed performance:

This process has an equal amount of output violating both specification limits, and the total number of nonconforming milk cartons per million is over ten times the goal. The process needs significant improvement.