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