Rational Subgroup
A rational subgroup is one in which the samples are selected so that the chance for variation due to special causes occurring within a subgroup is minimized, while the chance for special cause variation between subgroups is maximized. The key item to remember when developing a sampling plan is that the variation between subgroups is going to be compared to the variation within subgroups. Taking consecutive samples for the subgroups minimizes the opportunity for the process to change and should minimize the within-subgroup variation. The sampling frequency will determine the opportunity the process has to change between subgroups. The variation within a subgroup represents the piece-to-piece variation over a short period of time. Any significant variation between subgroups would reflect changes in the process that should be investigated for appropriate action. Source: AIAG SPC Manual

Random Sample
A sampling method whereby each service output in a lot has an equal chance of being selected.

Random Sampling
A method of looking at a few individual items in a lot to determine the quality of that lot against a standard.

Red Rabbit Test
used to check how long it takes to identify a defect. In this test, a red part is added to the mix and the time until it is discovered is identified.

Registered Suppliers
Registered Suppliers are suppliers who have received third party registration to a specific quality system standard for the commodity supplied.

Reliability
The probability that an item will continue to function at customer expectation levels at a measurement point, under specified environmental and duty cycle conditions.# of tests to pass - Confidence Reliability Reference - Pocket Card

Reliability Apportionment
See Apportionment.

Rengi System
formal decision process

Response Surface Method
a technique to find maximum or minimum condition - the basic strategy is in considering the graph (similar to contours on a topographical map) of the yield as a function of tthe two significant factors. The higher the hill, the better the yield.

Rework
Action taken on nonconforming product so that it will meet the specified requirements.