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 (σ^{2}): the mean value for all variables of the distance from x to mean, squared. Calculated as the mean of (Xμ)^{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