Variability and Randomness in Medical Research
Keywords:Predictability, random variability, statistics, systematic variability
In the present article, the first in a series of articles on the principles of statistics for surgeons, the ideas of variability and randomness in medical observations are developed. Variability can be partitioned into two components: systematic and random. The detection of systematic variability is the objective of scientific investigations, while random variability can be defined as the residual variability after systematic variability has been taken into account. That is, if the residual variability can be shown to satisfy, approximately, the statistical criteria of randomness. In the present article, we provide two examples in which the residual variation is shown graphically to behave like random variation. In practical applications, random variation should not be defined as having “no cause”. Similarly, randomness should not be defined as complete unpredictability. In later articles in the series, we will explore how the ideas of variability are used in medical research and statistical analyses.
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