Final answer:
Special variability refers to unpredictable and non-inherent variations in a system caused by identifiable external factors, distinguishable from common or random variability, which are either consistent or inherently erratic within statistical limits.
Step-by-step explanation:
A source of variation that is not inherent in the system and is not predictable is known as Special variability. This type of variability arises from factors that are typically not always present in the process and occur sporadically, leading to outcomes outside of the expected normal range. Unlike Common variability, which is inherent and consistent in a system, or Random variability, which is inherently unpredictable but often due to the inherent randomness in any process, special variability is due to identifiable, external causes that can potentially be corrected or controlled.
For example, Sample variability pertains to differences that arise when different random samples are taken from the same population. Unlike special variability, sample variability is still predictable within statistical limits because it stems from the random selection process of the samples.
Indicators of special variability can include irregularities in the object being measured or any other factors that specifically affect the outcome in a scenario, such as a machine malfunction in a manufacturing process or an unexpected event in an experimental study.