Measures of dispersion

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NEET PG High-Yield: Measures of Dispersion

Dispersion measures describe how spread out the data is around the central tendency. This is vital for understanding variability in clinical trials and public health studies.

Key Measures

Measure Description
Range The difference between the highest and lowest value; simplest but highly unstable.
Standard Deviation (SD) Most widely used; measures scatter around the Mean. $SD = \sqrt{\text{Variance}}$.
Variance Square of the Standard Deviation.
Interquartile Range (IQR) The difference between the 75th and 25th percentiles. Used with Median in skewed data.
Coefficient of Variation (CV) (SD / Mean) \times 100. Used to compare variation in two different units.
High-Yield NEET PG Pearls:

  • Normal Distribution: ~68% of data falls within \pm 1 SD, ~95% within \pm 1.96 SD, and ~99.7% within \pm 3 SD.
  • Standard Error of Mean (SEM): SEM = SD / \sqrt{n}. Reflects the precision of the mean estimate.
  • Skewed Data: Use Median and IQR (not Mean and SD).
  • CV: A lower CV indicates higher consistency or stability in the data.