Statistical variabilityStatistical variability is the term used in science to describe the fact that instrument measurements are often not perfectly precise and accurate. The consequence is that repeated measurements of the same quantity often result in data that differs slightly. When this happens, scientists usually assume that the quantity being measured is unchanging and stable, and that the variation between measurements is due to observational error.
This assumption may be false; the risk is that one ignores the possibility that the quantity is indeed dynamic and that the variation observed is intrinsic to the phenomenon. Naturally, the simpler model of a stable quantity is preferred when it is tenable, but the phenomenon must be examined to see if it warrants such a simplification.
For example, distinct members of a population may be observed which, ideally, one would like to consider interchangeable. Only in the arena of manufactured products is such a situation likely, and even there, the meticulous scientist finds idiosyncracy of sampled items. Hence, the differences between individual units become part of statistical variability.