Radiation Oncology/Medical Statistics/Distribution

Characteristics of Distribution

• Need to specify if variable is discrete or continuous
• Location:
  • Mean (μ): average value
  • Median: value that divides the probability distribution in half, meaning half of values are above it and half are below it
  • Mean and median are the same for symmetrical distributions, and different for skewed distribution. Extreme values of X influence mean much more than median
• Spread:
  • Variance (σ²): the mean value for all variables of the distance from x to mean, squared. Calculated as the mean of (X-μ)²
  • Standard deviation (σ): square root of the variance. Effectively the mean difference of variable x from mean
• Mean and standard distribution provide approximate distribution of the variables