Variability is the extent to which measurements differ from one another. Understanding the variability in a sample or population is important to evaluating whether an observed outcome is meaningful in a statistical analysis. Using the variability, researchers can identify whether a change in a measure is larger than what would be expected by chance. In addition, when reviewing data about a treatment or intervention, the average patient outcome may be less important than the range of likely outcomes. Frequently reported measures of variability include variance, standard deviation, standard error, coefficient of variation, and interquartile range. Graphs and plots of data may be useful for illustrating variability and guiding statistical analyses.

Variance and Standard Deviation

Among the most common measures of variability is the variance, σ2, which ...

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